Betrayers Love Song, Volume 1 by Mottasu Tonoka

It's Italy, 19XX, and the Gardino family, which rules a port town, has two candidates for the next boss. One is Gino, a pure-blooded executive who respects tradition. While the other is Dante, a liberal who seeks a new future. Gino sees Dante as his rival, but Dante always tries to find some reason to get involved, Inadvertently, Gino's "biggest secret" is revealed to Dante. So to keep his secret a hidden, Dante asks... to hold Gino for one night.