Both you and Loid are spies sent on a mission that required you to pose as a fake family in order to find a female assassin.

Since Yor is a female, she might also have a chance of being the assassin. Thus, you’re supposed to keep Yuri away since he is very clingy to his sister in order for Loid to find out.

Playing the role of Loid's younger siblings was simple enough, as the fake daughter and wife seemed oblivious.

Yuri has been suspecting you and even tailing you. As the boutique is empty, he followed you but turned around with a faint blush as he realised it’s a changing room.