Osana Najimi

'''Osana Najimi is the first official introduced rival for Senpai's affections and will be used as a tutorial at the beginning of the game. She is a student at Akademi High. Her AI won't be done for many months.'''

It should be noted that the character who stands under the left cherry tree closest to the fountain is Rival-chan. Osana in a future update will be completely different. Osana was changed because the original design for Osana had Rival-chan's adorable appearance, and YandereDev thought she wasn't tsundere enough. There is now a new appearance for Osana, while Rival-chan is the person with the old appearance; a different character.

She is not active yet because YandereDev wants to give her a different character model to make her more unique, but her character model is not compatible with all of the animations that were made for the female skeleton that the rest of the girls have. Osana can't be put into the game, unless a character rigger makes a control rig for her and an animator uses this rig to create a full set of animations for her, or if YandereDev gives her the same character model and animation as all of the other female students.

The downside of giving her the same character model as all the other female students is that she will look like a clone of Yandere-chan, but with different eyes, hair, and stockings. So far, YandereDev can't find anyone to get it done. It may be a while until she is implemented because the Dev doesn't want her without a whole bunch of Osana-specific "event" animations to go along.

YandereDev also has mixed feelings about Osana. Her current design is super cute but does not suit his opinion of tsundere characters. To balance this problem, he would either choose a personality that suits her cutest appearance, change her design so that it suits her tsundere status, or split her up into two sisters, a childhood friend and a tsundere childhood friend. He doesn't like the third solution too much because the death of one sister might affect the other so strongly that she couldn't consider dating.

Original
Osana's original look had golden brown eyes and her hair in two golden orange pigtails. Her hair was tied up in two plump scrunchies and she had a purple bow on her head. She wore white leg warmers. This appearance was given to Rival-chan, a stand-in for Osana.

Current
She is getting an update with long, orange twin tails that reach her thighs. The ends of her hair will have a small yellow gradient. Her hair will be tied up in thin pink scrunchies with white polka dots, and she will wear salmon socks with white polka dots. Her shoes will be black. On the reference picture of Osana, a small red bow can be seen on her head. A quick glance was shown, only showing the back of her in, "Dumpsters, Buckets, Bathing, and Electrocution in Yandere Simulator"

Introductions
In the original introduction of the game, after Yandere-chan bumps into Senpai, she can be seen talking to him, acting like a stereotypical tsundere. You can see the first intro on YandereDev's YouTube channel., but this is now very outdated.

In the second intro added in the August 15th, 2015 Build, Osana is mentioned by Info-chan as she requests for Yandere-chan to murder the girl. Info-chan expresses that she wants Yandere-chan to "make her suffer". It is currently unknown what Info-chan has against Osana.

Other
Osana had a small cameo in one of YandereDev's videos, "I Want My Senpai Back" She was the main antagonist of the video that stole Yandere-chan's Senpai. The tsundere was later killed off in the end of the video by being stabbed to death, possibly around 37 times.

Personality
Osana Najimi is a tsundere, which is a person that is very sweet and kind, but projects a hostile attitude to those around them, often only towards their love interest. It's not very likely that Senpai would know about her crush on him as she repeatedly insults him and seems oblivious. Regardless of Osana's rudeness and Senpai's ignorance, Osana is still very considerate. In the original intro, she is shown walking Senpai to school.

The second intro gives no indication of her personality, but "I Want My Senpai Back" makes her look like a tsundere, so she might still be a tsundere.

She may not be a good friend, considering that if you get rid of her non-lethally and Senpai's sister dies, she will not go back and comfort Senpai.

Senpai
They were childhood friends in the first intro. Osana has a crush on him, although he does not seem to be aware of it. The first opening shows Osana and Senpai together, and even walking to school with each other. Osana yells at Senpai, but they still seem close.

In the second intro, there is no information about what their relationship is now. Osana still has a crush on him though and will still confess her love to him on Friday. However, if Senpai's sister died then Osana, if eliminated peacefully, would neglect him so she probably doesn't care that much about him.

Yandere-chan
Osana Najimi is a target of Yandere-chan because she is a rival for Senpai's affections. In the first intro, Yandere-chan has qualms about killing others. She simply wanted a love life and Osana was in the way, but Info-chan, a glory-hungry journalist, gives Yandere-chan the idea to kill Osana.

In the second intro, Yandere-chan already wanted Osana out of the way, by any means necessary. Info-chan just encouraged her more and gave her some info.

Info-chan
In the first opening, Info-chan didn't hold anything truly personal against Osana. Still, it is now known that Info-chan was once the main antagonist who was going to be a rival for your Senpai, as seen on Info-chan's page. It is also known that in the original intro that Info-chan wanted some terrible events to unfold at Akademi High to boost her newspaper sales. It might have been one of the two, or both reasons, depending on when Info-chan was denied being the main antagonist.

In the second intro, it is not stated why Info-chan is going against Osana. Info-chan simply wants Osana to suffer, though anything about being a journalist is never stated. There isn't even in a Newspaper Club at Akademi High anymore, which greatly reduces the chances of her just wanting her articles to be popular.

Trivia

 * YandereDev has said that Osana Najimi is "Tsundere-chan with an actual design that had effort put into it."
 * Osana Najimi's name is a pun on "osananajimi," a common trope in the romance genre which means "Childhood Friend" in English.
 * In the video "I Want My Senpai Back", Osana is voiced by Brittany Lauda, who also plays Audrey from the popular adult game HuniePop.
 * She is the second tsundere character to be introduced by YandereDev, the first being Tsundere-chan from Kuudere Simulator.
 * In the final game, Osana will tease Senpai about how he stands under the cherry blossoms all day, a reference to how long Rival-chan was under her cherry tree.
 * It is implied on Twitter that Osana's birthday will be in January, most likely the 1st.