Homestay Harem wa Totsuzen ni!?: Itsuki-kun, Saikin Onnanoko to Sumi Hajimetandatte

Itsuki lives in a big house all on his own. One day, a foreign girl starts living at his house and things get steamy in the bathroom. Itsuki's childhood friend catches them in the act, and to Itsuki's surprise, she joins in on the fun!
(Source: Irodori Comics)
Note: Released at Comiket 97.