The fiancée of the tenth generation leader of Vongola is a loser.
"Tsuna! My box can't be opened T0T"
"Well, Momi... You didn't light the flame."
The sister of the fiancée of the tenth generation leader of Vongola is a female devil.
"Want to marry idiot Mo Mei? Did your head get caught in the door?"
"Nan, Miss Nanxiang, that idiot is your sister =-="
So, this is actually a story about a good-for-nothing who was lucky enough to be the fiancée of Vongola X, and a strong, brave and terrifying female devil.
——Wait a minute, did we forget someone?
"Tsuna!!!! My sister said that the killer is my sister!!!"