Kawaii no wa Zurui

A tanned gyaru in high school named Seina is in the middle of her summer vacation, when she finds herself temporarily taking care of a boy named Shouma, the son of her parent's friend. The mood is serious and seemingly quiet around Shouma, but they immediately become friendly with each other after she invites him to play.

"I love you."
Seina couldn't hide her confusion after hearing Shouma's sudden confession.

'What was that...?'
"I've loved you since we were kids. Since that day you first played with me."
Shouma snuggles up to Seina vigorously, and their bodies in close contact is the stimulus that causes him to have his first ejaculation.

Combined with the anxiety from this strange new sensation, Shouma, hoping to rely on her, repeatedly asks for naughty favors.
Seina tells him no, and while she feels reluctant about it, Shouma's audacious attitude overcomes her hesitation;
The number of times this situation repeats begins to pile up...

'It ain't bad...'
"Seina-san..."
'Think I'm in love with you...'

(Source: DLsite garumani, translated)