Senpai's Little Sister
|Strength||Incapable of self-defense|
She will look like a gender-swapped version of Senpai, which means that if Senpai is customized, she would have the same skin and hair color as him. However, she will have a unique hairstyle that no other NPC will have. At one point, it was made to look similar to Midori's original hairstyle, except that she had more bangs on her face.
Around November, her appearance was changed to her current design. She now has two pigtails that reach her shoulders, similar to the first drafts of her appearance. She has a red heart hairpin on the top right side of her hair and she has fair skin.
"Hanako is Senpai's younger sister. She loves her big brother more than anything in the world, and depends on him for almost everything. She is very possessive of him, and becomes upset when he won't spend time with her.
After nine weeks of gameplay, Hanako decides that she just can't bear to be enrolled in a different school than her beloved brother, and transfers into his school so that she can be with him all day long.
Hanako is deathly afraid that if her brother gets a girlfriend, he'll forget all about her and refuse to spend time with her. She has made it her mission to stop him from getting a girlfriend at all costs so that nobody else can have her big brother's attention. Senpai would never want to do anything that would make his little sister cry...this would spell doom for anyone who has fallen in love with Senpai."
Senpai's little sister was originally going to be cute and innocent, but she was later changed to lewd, jailbaity and perverted. These changes were intended so that the player would feel less guilty if she was killed.
His sister will remain in another city and school until the week when she is introduced. Since she will always be close to Senpai, it is presumed that she will have a similar routine to him. In order to eliminate her, the player will have to find a way to eliminate her during the few moments she is away from Senpai. If the player fails to eliminate the sister by Friday, she will force Senpai to promise to not get a girlfriend by the Confession Tree.
- Main Article: Senpai
Along with Osana, she and her brother used to play together when they were little. She doesn't lust after her brother, but loves him to the extent that she does not want him to get a girlfriend. She wants all his attention, and does not want anyone to divert his attention from her. 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.
If she convinces Senpai never to get a girlfriend, she will eventually develop into a self-reliant, independent person, who won't rely on Senpai. 
If she ever got a boyfriend, she would become independent from Senpai and he would be happy for her.
- Main Article: Osana Najimi
Hanako and Osana have known each other since they were children and used to play with each other alongside Senpai when they were little. Osana might be the only person that Hanako would be willing to "give" Senpai to. Hanako wouldn't really look at Osana as competition, or a threat, or an enemy. Hanako would be very sad if Osana died.
- Similar to her brother, her name is the Japanese equivalent of a "Jane Doe".
- If a week long culture festival were to added into the game, YandereDev has stated that Hanako may be the rival of this week.
|“||Welcome home, big brother! How was your day?! Tell me ALLLLL about it! ...if you got a girlfriend...would you forget about me? That won't happen, will it?!||”|
— Hanako in "Yandere Simulator Rival Introduction Video"