Comment by 4hja on Sss-Class Suicide Hunter - Chapter 120

Lefanta was a really bad bullying victim back in Korea. Gongja becomes "immersed" as a character in his memory after they fight and Lefanta kills him. he basically lives as one of Lefanta's classmates with every person (except Lefanta himself) in the memories being replaced by someone Gongja knows irl (ex the classmate's gf becomes Laviel)

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Lefanta's real name is Kim Yul. in school, his bully, Hwang Eunseo, did everything in his power to make Kim Yul's life miserable. there was only one person in the school who cared for him, but was too nervous to actually speak up about it. this was revealed to actually be the director of the orphanage Gongja grew up in.
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Kim Yul jumps from the top of the school building and then reincarnates as Lefanta Aegim in the Tower. 

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Gongja then helps Kim Yul gain closure by making the 29th floor of the tower basically a redo of Kim Yul's school life (thanks to the creepo Librarian). 

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Gongja fully immerses into Hwang Eunseo (the bully), so the orphanage director (who entered the tower a little earlier) & Kim Yul work together to get their get-back and clear the 29th floor.