She lives with her mother while in elementary school.
While acting strong and not worrying about my mother, a half-boy who lives next door
'I will be my brother' Thanks to him for promising me, his loneliness was mixed.
In school, he always fell in love with Noah, who was close to him than needed, and Hikari was mocked by her sister.

She becomes a college student, and her mother and Noah's father are officially married!
I'm happy, but both in name and reality, Noah and 'brother' I am shocked that it will end up.
But Noah's skint gets more intense, finally kissing her lips, her tongue in...?
篠宮ひかりは、小学生の時に父親が出ていき母親とふたり暮らし。
母を心配させまいと気丈に振舞っている中、隣に住むハーフの男の子・ノアが
「自分が兄になる」と約束してくれたおかげで寂しさは紛れていった。
学校でも常に一緒で必要以上に距離が近いノアに、いつしか恋していたひかりは妹扱いにモヤモヤ…。

大学生になり、片親同士のひかりの母とノアの父が正式に結婚！
喜ぶひかりだが名実共にノアと「兄妹」になってしまうことにショックを受ける。
しかしノアのスキンシップは一層激しくなり、ついに唇にキスされ、舌も入ってきて…？