Futarijime Underdog

Futarijime Underdog summary:

After Mutsuki's father's company goes bankrupt and they become poor, Mutsuki's got no choice but to pick up multiple jobs. One day, popular twin models show up at one of his convenience store jobs and offer him work that sounds too good to be true. He jumps on the chance and moves into their place to work for them. However, there is a clause in the contract that he missed when he signed it...! The twins turn out to be the two boys Mutsuki bullied when they were children... so they put a collar on him and spend every day getting their revenge on Mutsuki.