oh gosh that is a good question. obv this is all speculation on the part of Kir, but I know Ny wants to have e v e r y  s u b [within reason] and if he takes an interest in someone he will Want Them.

and Kir is very full of himself, very haughty boy, I think to Ny he’s just begging for a strong hand, which is basically Ny’s favourite thing he loves working with subs to improve them, he likes turning nervous and disobedient subs into good pets

so I would imagine that Ny was on one of his stately visits, you know how he do, and he probably wasn’t looking for a new pet, but then this cute, proud little naga shows up and starts putting on the moves and Ny is like [: and shows him how to be a proper good boy

I imagine afterwards it would be Kir who comes back to Ny, wanting to be inundated into his service, and Ny wasn’t planning on taking any pets home with him but this one needs him (spoiler alert everyone needs him Ny is to subs what will graham is to dogs) and he can’t help himself but accept Kir on (making sure Kir knows this isn’t going to be some lounge gig, he’s gonna have to work to be a good sub)