I actually read this one some time ago but I'm trying not to spam you guys too much! There are actually short different stories in this one but what I like the most about it is the unusual style...

Shiranu wa Omae Bakari

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Synopsis: Yoshikawa Taiki and Komiya Kazuyuki had sex once almost every week, but they were neither lovers nor friends. What started off as a drunken escapade back during a university get-together scaled into something bigger than either of them could have imagined.