if I remember correctly, it might be taehee former name (?)
the next season might show Taehee back story
Aww tysm
HUGE SPOILERS
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Remember when Taehee talked about the exorcist who tried to steal the talismans and got set on fire because of the spell? That man actually did it because his son, Yeono Yoon, was exorcised after he brought his son's spirit back (after his son died). His colleague thought it was a ghost that needed to be sent away when his son wandered outside, and the colleague destroyed it, so the exorcist tried to get revenge and failed.
He went into the mountains and begged the gods for something to get his revenge on the exorcism agency, and that was how Taehee was born.
Taehee essentially became a pseudo-son for the exorcist, and he called him grandpa, I believe.
Who's seono yoon