Nack didn't even forget the two years of constant bullying by Mina. But what do you expect he would do? do the same two years of bullying to do the same? Unlike others here, Nack had overcome his fears, growth his self-esteem and experiencing such a hellish and gruesome training much worse than the 2 years of his life, Mina's constant abuse was viewed as less terrifying, even pity at that. The fact that he won at the end, and did not forget his training where he would absolutely saved everyone AND himself. Again Nack didn't forget the 2 years of being in pain, but it remains evident that he has self-esteem.
The person saying flirt? That's a virgin take. You don't clearly see him getting blushed. If it's me, I'd interpret it as something more as a conviction that he will never ever lose to Mina. Not everything is about romance -_-
