She was implemented in the November 15th, 2015 Update, just not currently as the rival, as Kokona Haruka is still the current rival. She is the founder and president of the second Occult Club at Akademi High.
She will not be present at school for the first few weeks. While she is absent, a member of the Occult Club will be her substitute. The substitute will allow the player to join the club and participate in club activities while the leader is absent. In the debug build, the player will be able to see Oka walking around, but in the final game, she won't appear until several weeks have passed. Her current features are also temporary and will change in the future.
Oka has messy, shoulder-length hair. She has a fringe hanging down the middle of her face. Her hair is dark blue. Her eyes are light purple. Around her eyes, she has large black rings due to lack of sleep. Her lips are pale, and as is her skin. Her bust size is 1.
Some of her appearances can be seen on Druelbozo's account on DeviantArt. He has made some other stuff for Yandere Simulator, as stated by the Dev. In her second look, her hair is much messier. Her hair is also a darker shade of blue.
Oka wears the same default uniform as all the other female students, unless customized by the player. She also wears knee high dark grey socks.
She walks very slowly, with her hands clasped together. She is always looking shyly at the ground. In the future, she will have very pale skin.
Oka is a stalker, but not a yandere. She is too shy to harm others. Her mannerisms make her look shy, timid, and socially awkward. She is obsessed with anything paranormal, even since early childhood. 
Among the personas within the game, Oka is a loner. If she witnesses a murder, she will flee home and call the police. She will not fight back if attacked. It is unknown whether she will be given a different personality later on in the game, due to her being a future rival.
At 7:05 AM each day, Oka will enter the school grounds. She walks to her locker at 7:10 AM. At 7:15 AM she will head up to the rooftop and stalk the Basu sisters until 8:00 AM, in search of proof that they are actually supernatural beings.
At 8:00 AM Oka will walk into Classroom 3-2 and sit in her desk. She will start class at 8:30 AM and will leave to go to lunch at 1:00 PM.
Since she is an average NPC and not a rival yet, she will have no special events, so she will go up to the rooftop on the southern side, and watches the Basu Sisters talk to each other once again.
Oka walks back to class at 1:30 PM and will finish second period at 3:30 PM. She will then go to her locker and linger there until 3:50 PM, when she walks to the Occult Club room. She will stand in the middle of the pentagram until school day is over.
The Basu Sisters
Since she is a rival, she will have a crush on him, and will confess to him on Friday. Oka is a very superstitious person, and that might play a role in the way that she develops a crush on Senpai.  Since she is very strange, the way they will meet will be comical. YandereDev would not like to reveal anymore through Twitter.
As announced by Druelbozo, Cho Shizen will also be a member in the occult room. It is currently unknown what relationship they have.
- Her favorite Creepypasta is anything popular on Japan's internet in 2016.
- She has an anxiety and paranoia problem.
- Oka's dark secret is related to the reason why she is absent from school for the first few weeks.
- She is one-third Hex Maniac from Pokémon X & Y and Pokémon Omega Ruby & Alpha Sapphire, one third Tharja from Fire Emblem: Awakening, and one third Tomoko from No Matter How I Look at It, It’s You Guys' Fault I’m Not Popular! (can be shortened to WataMote).
- Oka's name is a play on the word "Occult" in Japanese Katakana, Okaruto (オカルト)
- YandereDev finds Oka very cute.
- Oka was first created through a suggestion thread. In one of the first "suggestion threads", someone pitched the idea of a goth girl rival. The girl who first popped into YandereDev's head was a cute shy girl.
- It may be possible in the future that if Oka is killed, she will be visible as a ghost after death.
- One of Oka's elimination methods may involve the Phantom Girl. 
- Oka has played Corpse Party before.
- If you kill her in the Occult Club, dark music will play in the background.
- If the Basu sisters are missing from their meeting spot, Oka will continue to stalk the area where they once were.
- When asked to go to the fountain, she will do her stalking animations on the fountain until it is time for class.
|“||...s-she's...p-probably...a s-special vampire...w-who can survive in the sunlight...t-this requires...f...f-further research...||”|
— Hypothetical dialogue if Yandere-chan told Oka that Inkyu Basu can be spotted in sunlight.
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