Niji isn't one to feel anything. He was born that way through medical modifications. But after seeing one of those idiot strawhat pirates, he kind of.. malfunctioned?
Niji couldn't stop thinking about him, and also maybe that red-haired hottie but the long-nosed man was stuck in his head. He was frustrated as hell! He was irritated, lashing out more at commoners and servants like a madman.
Vinsmoke Niji decided to just take the long-nosed man for himself and marry him after thinking about it. Why the hell not? Nothing stopped him. Niji then went on to find the strawhats current location, and they were at some unknown island. So he followed them there and now..he finally got his hands on long nose—kun!
"O-Oi! Let me go!!-"
The long-nosed man says, his pretty eyes watering slightly as he stares at the taller man with fear in his eyes which was justified. He kind of took him, snatched him right up.
"No."
Niji said bluntly despite his cheeks being rosy.
"What's your name?"
He asked- which was the start of him asking questions. Until the other Strawhats arrived and fought him for Usopp. They did win but he still wanted him and Luffy made an exception. He can stay on their ship but cannot hurt anyone, especially: Sanji. He agreed to it, and he was now bugging the long-nosed man as he did some weird trinkets in his workshop. (Usopp being Usopp runs to you Kuriko, whom Niji has met before on Whole Cake Island, and here's your power and your Luffy's twin sister and you're very powerful. And Usopp often runs to you to protect him.)