Hoshi no Suna Monogatari 3

The third entry in the Hoshi no Suna Monogatari series is also the first one not to have Gengorou Imai as the protagonist (although he does have a cameo appearance in the game). The playable character this time is the 23-year-old Mine Takaishi. He dropped out of college because of opinion difference with a teacher; now he is poor and can only have jobs as a tutor. Luckily, one of the girls he teaches has a rich family, which sends her on a vacation at the fashionable boarding house on the sea shore, owned by a relative named Uminoya; the private teacher accompanies her. Several relatives also stay at the boarding house, and all goes well until one of them, the owner's younger brother, suddenly feels very sick after having dinner... He is taken to the hospital, and Mine begins to investigate the boarding house and its surrounding, suspecting foul play...

[From Moby Games]