Asuka (u) the older step brother of Yui (s).
At summer where Asuka (17) and Yui (12) they were at the "secret base" . And during that day Yui was ignor ing Asuka.
When Asuka jerked off in his room, Yui see him and said "what a dweeb". That make "the little Asuka" cannt get up anymore!
In the middle of ch 1 they make up and become lovee.
The whole ch 2 filled with about their relationship.
Brother (Ougi Yuzuha)