Sizin 

1. To have lots of girlfriends or boyfriends
2. To take other's girlfriends or boyfriends

Kim is sizinning around, which made his ex-girlfriend extremely angry.

Sizin by None other human May 7, 2018

Seizing 

A 14 yo kid who plays critical ops. No doubt the best sniper in Asia.

Seizing literally 360° flicked noscoped him.

Seizing by Noicing all the way June 12, 2020

Seijin 

Seijin, which refers to humanoid aliens from space, means a ‘Person from the Stars’ in Japanese.

Ultraman is the most popular Seijin in both Japanese popular culture and the pop cultures of many nations in general.

Seijin by Snapper2001 May 15, 2023

oppai seijin 

Person who loves big tits (esp. anime titties)

Pedestrian oppai fan: Bro did you play this god tier nukige called oppai academy?
Based loli enjoyer: I ain't no oppai seijin ya dipshit. I only play lolige.

oppai seijin by pyun pyun April 14, 2022