I don't know😭😭 what is that???

Hwan put chiwoo into a dream world, this happened because Hwan was jealous of Jin that living with Chiwoo. after that Jin approached Hwan, and saw Chiwoo trapped in a crystal?(idk how to say it) Hwan wanted Jin to disappear forever as a condition for releasing Chiwoo. Jin agreed and prepared to be eliminated but Chiwoo woke up at the right time and protected Jin. But in the end Jin sacrificed himself and was hit by Hwan weapon, after that Jin disappeared as if he had never existed in this world

What is sa sangyup???