Akane-iro ni Somaru Saka (OVA)

This OVA is a side story to the main arc.
Junichi Nagase and friends get an inviation to a luxury holiday from Karen Ayanokouji on her private island. Up to the point where the girls try out the school representative's new suntan lotion, everything is running fine for Junichi. During the night, the suntan lotion is causing miscellaneous adverse effects which entice the girls to seduce Junichi, who in return is trying to escape his harem.

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Everybody goes on vacation to Ayanokouji's private island for fun in the sun. Hilarity ensues.

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Jun'ichi and his friends have been invited to vacation on a private island during the summer. But while everyone expects pure-hearted fun in the sun, Mitsuki has other plans! Now the Geno Killer is in for a ride as Mitsuki's sunblock aphrodisiac gets all the girls ready for action. Jun'ichi must struggle to keep his pants on, lest the desires of the women around him become too much to bear!