Utakata no Tsubomi

Kotaro Izaki, the protagonist who returns home at his older sister's request.

Kyoko Miura, the recently widowed older sister who is terribly lonely.

Expressionless and standoffish since childhood, an old classmate named Miyuki.

Tomoe, the defiant blonde bad girl.

These four players form a homecoming story around Kotaro,
spurring days of lewdness......

[From DLsite English]