Is Stringendo+Accelerando Ultimatum Sera hentai?
Yes
Rated Rx (Hentai) on MyAnimeList.

OVA · 2008 · 3 episodes · Rx - Hentai
Hentai
School is a place for learning and gaining knowledge for the sake of the future but very few know of what happens between couples/students behind the scenes which could be considered learning but in a more intimate way. (Source: ANN)
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