Two Player Game

Ren and Natsuki have been childhood friends since before they can remember. When Natsume was a child, he was taught to masturbate, which led to him being able to ejaculate only with Ren's hand. As they continue to comfort each other without kissing or having sex, Natsuki finds himself falling in love with Ren.

(Source: Takeshobo, translated)

Note: Include one extra chapter.