Otona ni Naru Natsu: Oboetate H ni Dohamari suru Inaka

The main character, Souta, is sent to the countryside for summer vacation because of his mother's childbirth. When he meets his cousin Shino for the first time in a long time, she hugs him and welcomes him enthusiastically. Souta is depressed about his life in the remote countryside, but as Shino shows him around the village, he gradually begins to open up to her... However, they accidentally fall into a rice paddy and go to the bath to wash themselves. Souta gets an erection involuntarily when he sees Shino's tits soaking wet and transparent. Seeing this, Shino gets aroused and starts licking Souta's penis...? Souta climaxes for the first time in his life, but he is unable to cum because he has not yet cum. Shino is instead drenched in the pee that comes out, but she is so aroused by it that she is confused about it herself. Then their love and sex heats up...

(Source: DLsite, translated)