https://www.dlsite.com/comic/work/=/product_id/BJ310516.html
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I can't do it here, but... All the bad things that hit my ass are bad...

"I can't stand it if there's something like this right in front of me..."
Natsuki persuades her boyfriend Masahiko, who is not good at sports, to go to the pool with her.
Masahiko, who can't swim to begin with, is supposed to train in a kiddie pool, but Masahiko is not interested in swimming and is only interested in seeing Natsuki in her swimsuit.
Masahiko's hardened cock is pressed against Natsuki's body, and the two get into mischief in the water, which turns Natsuki on.
Masahiko's hard penis was pressed against her and she was being played with underwater, and Natsuki gradually became aroused as well, and secretly started servicing her with his mouth...

Very nice, hope the other chapters are uploaded soon

Base +8