A Japanese name meaning "a moment;an instant", can also be translated to "calm snow", it originated from India meaning smallest unit of time in which a piece of consciousness moves. It is used in sentences to describe a momentary thing that was for a short time but was a good experience.
person A: whoaa who's thatrunning around, they're so fast!!
person B: yea, thats setsunasupremacist. she's doing her daily roundabouts around the world after seeing a sen kaibara post on tiktok.