Sekai has several positive relationships, countering the several bad relationships Kotonoha has.
Sekai lives alone with her mother and appears to be close to her. She has learned a lot from her mother and often confides in her when she is able to.
She despises her Father for his lecherious personality and abandoning their family.
Initially Sekai tried to help Setuna hook up with Makoto until she developed feelings for him. Realizing this Setsuna stepped down to allow them to get together, but Sekai found herself unable to approach Makoto. By the time she finally could she realized he had feelings for Kotonoha and attempted to pull the same stunt and used this to steal his first kiss after they officially hooked up.
Normally Sekai shows a tsundere-like personality and temper that doesn't appear around others. The entire time she was willing to allow him to do whatever he would like to her, and she shows no shame if it meant getting him to noice her.
Unlike the other girls Sekai held no ill-will towards her, other than a tiny amount of jealousy over her big chest. At first she genuinely seemed to like Kotonoha and wanted to be her friend, and after she started to grow closer to Makoto she had wanted to come clean to her straight away and would try to avoid the both of them to let things work out.
She was remorseful over her actions, but in the Anime and Manga she is shown to lash out at Kotonoha and ends their friendship or what was left of it by that point.
They can become a threesome with Makoto in a spin-off manga and in one route of the original game.
As they have been long-time friends they are bonded closely. They rely on each other emotionally and struggle, breaking down if one was to leave the other alone. They actively tried to help each other win Makoto at different points in life and as said, Setuna is highly protective over Seika and believes they are already together.
Nanami and YukariEdit
Her good friends from school who she is often found with during it or outside of it. She was shocked to learn they were Kotonoha's bullies, along with Otome. They indirectly cause Makoto to hate Sekai in one ending of the game, as he heavily dislikes bullies and believed she knew about it.
A young man who likes Kotonoha and despised Sekai, blaming her for ruining her happiness with Makoto- even though he doesn't like Makoto either. In the game, he can attempt to murder her or rape her.
In the spin-off manga featuring the game, she tells him to mind his own business as he eventually learns she is in a threesome with Makoto and Kotonoha.
Makoto's friend and someone she can end up with in the game depending on route choices when he accidentally rapes her, having been told by Otome that girls like forceful guys. She appears to feel nothing for him but is lonely enough to accept the sexual relationship, although she appears on good terms with him on certain routes otherwise.