Senpai (A.K.A Taro Yamada) is the obsession of Yandere-chan.
NOTE: At the moment, Taro Yamada is a placeholder name. Taro Yamada is the Japanese equivalent of "John Doe". John Doe can refer to a hypothetical person whose real identity is unknown. His name will be never spoken aloud, but it will only appear in the Student Info screen and in the fictional social media. The player may be able to pick what Yandere-chan's Senpai's name is in a future update. 
In the first intro cutscene, he was first seen in Yandere-chan's dream, where the player can customize him. The next morning, Yandere-chan, who was late to school, bumped into him and ever since she has been obsessed. Senpai, however, does not know this, and will accept the love confession of any girl who chooses to do so. Right after he meets Yandere-chan, he is scolded by Osana Najimi and they walk the rest of the way together, with a lamenting Yandere-chan watching from afar. Info-chan watches the entire scene from behind.
In the second intro, Senpai is merely mentioned, if you don't count the part where you customize him. Info-chan calls Yandere-chan out on stalking an upperclassman, and tells her that the girl he was with is named Osana Najimi.
Appearance (Default Look)
Senpai's original gender is male, therefore, the article will refer to him as such.
Senpai, in his default look, has short, messy dark hair, charcoal gray eyes, light skin, and the default male school uniform with gold buttons and black coloring. This is his default look because he is meant to look like a plain, average, generic, everyday male protagonist, which is the type you see in hundreds of anime.
During Yandere-chan's dream at the beginning of the game, you can customize his eye color, hair style, hair color, skin tone, gender and eyewear, but if no changes are made/the player skips the process, then Senpai will appear as his default look. Senpai is as tall as everyone else in the game so all animations can link up. If possible, YandereDev would wish for Senpai to be slightly taller.
As of the August 15th, 2015 Update, you can customize Senpai again. When you start a new game, you are asked whether your ideal lover is a boy or girl. Since the female Senpai hasn't been implemented yet (and won't be for the next couple of months), the player must choose to have Senpai as a male student. A female Senpai can be made through modding, but they will still have a male voice for certain things. The starting screen has the default Senpai, but naked with steam covering his private parts.
The default Senpai has skin color #3, hair style #1, hair color #1, eye color #1, and eye wear #0.
Shades from very fair skin, to dark brown. Five skin colors are available.
Default (#1), hair similar to Haruto Yuto (#2), hair similar to Sota Yuki (#3), hair similar to Hayato Haruki (#4), hair similar to Ryusei Koki (#5), hair similar to Sora Sosuke (#6), hair similar to Riku Soma (#7), and bald (#8).
Hair colorLight Grey (Hair Color #1), Red (Hair Color #2), Yellow (Hair Color #3), Green (Hair Color #4), Teal (Hair Color #5), Blue (Hair Color #6), Purple (Hair Color #7), Black (Hair Color #8), and as of September 20th Build, Orange (Hair Color #8) and Brown (Hair Color #9). (Note that the Default hairstyle's coloring is considerably darkened compared to the other hairstyles.)
Eye colorBlack, Violet, Indigo, Teal, Green, Yellow, Red, Gray and as of the September 20th, 2015 build, Orange and Brown.
Nerdy dark grey glasses, thin wire glasses, red thick glasses, 3D glasses, and shades.
If Senpai is a female, then you will be able to customize her bust size and stockings, as well as the other customizable options of male Senpai.
The first intro portrays Senpai as kind and considerate. He cares for Yandere-chan when he bumps into her and is seemingly friendly. He doesn't hate Osana Najimi for being rude to him, and just follows her orders.
Senpai doesn't act too shy. When he bumps into Yandere-chan he doesn't get flustered in a sheepish manner. He just shows concern for the girl he just met. He seems to be a loner of his own accord, though we have no records of him trying to be popular or disliking not being at the top.
He's also a pushover. Senpai doesn't stick up for himself against Osana and will accept any confession of a rival, which is why there's a deadline.
The second intro's Senpai doesn't nearly have as much characterization as the first. His personality is never even mentioned by Yandere-chan nor Info-chan. He still will accept the confession of any rival with a good enough reputation, which might imply that he's still just a bit of a pushover. However, this could be just because he's on good terms with all the rivals.
His personality will be shaped and molded by the way that people around him are disappearing. If rivals are matchmade with suitors, Senpai will think that he is not appealing as other boys are. If girls mysteriously stop coming to school, then he will assume all girls who skip school are delinquents. If girls show up dead shortly after they talk to him, Senpai will wonder if he is cursed. Depending on your actions, Senpai might develop PTSD, a personality complex, a nervous disorder, or social anxieties.
He seems oblivious to Kokona's affections, judging by how she laments he never notices her feelings when talking about him, formally at the rooftop, but currently in the courtyard at lunchtime. Senpai never seems to realize why Yandere-chan follows him around and just shouts at her to leave him alone.
He is a loner who enjoys nature more than the company of people. Though an introvert, he does not seem to be shy. Senpai is not popular in the beginning, although girls will fall in love with him over the course of the game. Some popular people might even notice him.
He is an average male who gets average grades.
A backstory for Senpai has never been fully written for him. He's meant to be plain and average.
In the original opening cutscene Osana Najimi was his childhood friend. They have known each other for a decade, it seems.
The reason why he is so popular is because he sat in the "Main Character Chair". From that moment onwards, his fate and destiny were set in stone.
Senpai has a little sister. She will look like a gender swapped version of Senpai, but she will have a hairstyle that no other NPC has.  His parents look very plain. The dad looks like an older version of his son, and the mother looks as plain as her son looks.
Info-chan cannot dig up any dark secrets about Senpai because he is spotless. He has no dark secrets at all. 
At 7:05 AM each day, Senpai will enter the school ground first in line on the left to school. He walks to his locker at 7:10 AM. At 7:15 AM, he will sit on the fountain. He doesn't talk with the other students.
At 8:00 AM Senpai will walk into Classroom 3-2 and sit in his desk. He will start class at 8:30 AM, and will leave to go to lunch at 1:00 PM. During lunch, he does not eat, but will sit in the plaza on the fountain. Kokona Haruka will watch him on Wednesday.
Senpai walks to class again at 1:30 PM and will finish second period at 3:30 PM. He will then go down to his locker and later linger there until 3:50 PM, when he walks home.
During the game, Senpai will walk around or sit on the base of the fountain while the other students gossip.
Staying near Senpai will cause Yandere-chan's heart to beat loudly and the screen to turn pink. Yandere-chan will drop what she's currently holding, keeping her hands to her chest. She cannot do anything besides walk when she's near him. Entering this pink zone will help her recover lost sanity. In the future, Yandere-chan's animations near Senpai change. They will look much weirder and her appearance will change into someone who is extremely anxious.If Yandere-chan stands in Senpai's line of sight for too long, he will get slightly freaked out, and slowly lose patience. If this happens five times in one day, he will yell at her, telling her to go away, causing Yandere-chan to become heartbroken and trigger an immediate Game Over.
If he sees Yandere-chan performing suspicious actions such as having low sanity, holding a weapon, dragging a corpse, being covered in blood, or killing a person, it will trigger an immediate Game Over as well.
Since Senpai is a Loner, he will run away when he sees a corpse on school grounds, if Yandere-chan is not there to alert him in some way and get a Game Over.
Senpai will have a hidden sanity variable that will influence some of the game's endings and might influence his everyday behavior.
In the full game, Senpai will be on good terms with all the rivals, so if he sees them bloody he'll go easy on them. Still, if there's too much "evidence" against your rivals then he can't help them out.
In the first intro she is his tsundere childhood friend who would berate him. Senpai just stood there and took what she gave and will still accept her confession, so long as Yandere-chan doesn't mess it up. In the second intro she is still the same old tsundere friend.
It's not revealed why Senpai chooses to hang around Osana after all this time. After she is eliminated there might be a cutscene showing how Senpai is handling the situation. 
Before meeting Senpai, Yandere-chan was just drifting through life without any purpose. Yandere-chan only met Senpai a few days before the game begins and she changes as she no longer cares about right or wrong like she did before the encounter.
Yandere-chan acts like a pervert toward Senpai, wanting to go into the Boys' Shower Room to see admire him. Even so, what she feels isn't lust, but more like seeing color in a grey world. In fact, it might not even be romantic, since Senpai just seems to give Yandere-chan new sensations.
If she ever accidentally hurt Senpai, she would feel a mixture of depressed emotions. However, Yandere-chan is okay with mentally traumatizing Senpai in order to eliminate a rival.
Yandere-chan couldn't object to anything that made Senpai happy, so long as it isn't another girl. Because of that, Senpai could use her if he wanted. However, if he insulted her she'd punish him and maybe even break him to fit her ideals.
Senpai isn't close with Yandere-chan and he doesn't know much about her. He usually never notices Yandere-chan as she can stalk him after school, depending on how the day went. However, if she stands near him for too long during the day then he might notice and get freaked out.
If Senpai was ever killed and Yandere-chan knew who did the deed, she would feel a cross between deep hatred and total, hollow emptiness. If Senpai ever committed suicide because of Yandere-chan, she would do the same.
Info-chan doesn't care for Senpai's love life. The two never seem to interact and Info-chan is perfectly fine with ruining his life, whether it's to boost her newspaper or have her for herself (first intro) or to just get rid of an enemy (second intro). Info-chan might not also care for the other rivals because she'll still help Yandere-chan get rid of them, even if Senpai has a chance of being very happy with them.
Info-chan will not accept your photos of Senpai, should you send them to her.
Senpai is oblivious to the test rival Kokona Haruka's feelings. They are in the same class as each other, yet she still calls him Senpai.
The Imouto is his little sister. She is a planned rival, but not because she lusts after her brother, but because she loves her brother to the extent that she does not want him to gain a girlfriend. She wants all his attention. She is also extremely clingy, possessive of him, and would never want to leave his side.
If she is killed, Senpai's sanity variable will greatly decrease.
At the end of the sister's week, she will force her brother to agree that he'll never get a girlfriend.
Eventually when Yandere Simulator is finally released, Senpai will become sick for the one week the Nurse is in. He will visit her once every day. Senpai will become attracted to the nurse, and their relationship may grow.
|“||What's up with her?/She's acting strange.../That girl is kinda weird.../She's starting to freak me out...||”|
— Senpai after he spots Yandere-chan harassing him.
|“||Hey, cut it out! That's really creepy! Leave me alone!||”|
— Senpai after being harassed too long.
|“||What the hell is wrong with you?! Get away from me!||”|
— Senpai after seeing Yandere-chan visibly insane/ laughing manically.
|“||Why do you have a weapon? What are you going to do with that thing?! Stay back!||”|
— Senpai after seeing Yandere-chan visibly armed.
|“||Why do you have so much blood on you? Did you hurt somebody?||”|
— Senpai after seeing Yandere-chan covered in blood.
|“|| You killed them! Stay back! Get away from me!/What have you DONE?! You MONSTER!/Oh my god! You just MURDERED someone!/How could you do that?! Do you realize what you've just done?!/This can't be happening! Somebody, help! HELP!
— Senpai after seeing Yandere-chan murder someone or near a dead body.
|“||What the hell are you doing? That's horrible! Stop that right now!||”|
— Senpai after seeing Yandere-chan taking panty shots.
- Senpai's favorite food is still undecided.
- Senpai's reactions and voice may remind some of Amano Yukiteru from the anime Mirai Nikki (Future Diary), the original inspiration for the Dev to make the game.
- Senpai wrote a book, "How to Hentai without Hentaing", seen in the May 7th, 2015 Update. This feature was later removed; This has been proven as non-canon by the Dev.
- As of the September 20th, 2015 Update, when Senpai witnesses Yandere-chan commit murder, all students will freeze in place and look at Yandere-chan in horror.
- In old builds, Senpai was usually the first to naturally witness Kokona Haruka's corpse if you poisoned her at lunchtime as he formerly stood closest to where her corpse would be, and would spot her corpse as he headed back to class at the end of his lunch break. However, since the November 15th, 2015 Update, Kokona's corpse is no longer in Senpai's path as he returns to class, and he will not discover it.
- Unlike YandereDev's video where the features of poisoning Haruka was added, Senpai's voice lines for that event were not in the actual game like "Is that a dead body? I have to tell a teacher!"
- Senpai currently has no voice acting for when he catches you taking panty shots although he does react.
- Senpai is one of the only male students that is a Loner, formerly along with Ryuto Ippongo who switched to Teacher's Pet in the October 8th, 2015 Build. If he spots a corpse, he will run home and call the police. He only tells to the teacher instead after witnessing a poisoned corpse, but it should be noted that all students will do that.
- You can get the character model that was used to make Senpai in the Unity Assets store.
- Senpai was voiced by Austin Hively in "I Want My Senpai Back".
- In an upcoming update, you will be able to steal Senpai's clothes and shoes from the gym. If this is for the Senpai Shrine then this kind of stealing from Senpai has been planned the whole time.
- In Japanese, "Senpai" literally means upperclassman.
- The only way to kill Senpai is to shoot ice at him in Cirno Mode. The only way to drag him is to shoot him while he's near the top of some stairs so that he falls away from the aura, which stays where he originally died.
- If Senpai was in a Hogwarts house, he would be a Hufflepuff. 
- There are 24,000 different combinations for Senpai. 120,000 different combinations if Senpai is in a customized uniform.
- Senpai has never bought a panty shot from Info-chan.
- YandereDev would like female Senpai to look like a girl with medium-length black hair with fair skin.
- Senpai has an unnamed career path that has not been revealed yet.
- Senpai can probably cook a few simple meals. 
- When viewing Akademi High School's Facebook page, there is a post made by Senpai asking how old the sakura trees are.
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