Basically a flashback from MC who wakes up from a dream of the past 5 years ago when he found his GF childhood friend cheated on him and likely ended their relationship, flashback shows ntr guy fucking the teacher as soons as he join classes and Mio catches his interest and lust and conveniently blackmais her into becoming his cumdump behind her bf aka MC's back. I wonder what intends the author to show on his story, MC already got cucked and is a mess 5 years later. Hopefully it shows him moving on instead of draggin the story.