Se-hun

nacho and cosmos dad bad man, he would later go on to father many children with another woman which would later go on to produce ming yue long down the line as a result. Se-hun was the person who gave nacho hakkuns book because he wasnt sure what it was after finding it amongst the towers stuff(and maybe in-su left a note that would have kept those not worthy from touching the book unless your nachos dad and you dont care about the villages history and stuff man)