Lover-in-Law(兄嫁はいじっぱり)

Tsutomu's parents passed away several years ago, before that they ran a flower shop. Now it's run by his older brother's wife, Mai and he is living with them. Tsutomu's brother now works somewhere else, so Mai is left alone and her only support is Tsutomu, who helps her running the flower shop. Because Tsutomu's brother is busy and haven't been home for a while, Mai feels very lonely which Tsutomu notices and decides to support and satisfy Mai while his brother is away. Now there's also Kozue, Mai's friend and senpai who recently got hired as part-time worker. Kozue has noticed Tsutomu and Mai's relationship and she envies them because she is also very lonely, because her husband is rarely home. Mai sympathizes with Kozue and allows her to date Tsutomu. Now what will happen as these three indulge themselves to their desires and feelings?