ok.. yes, kisaki now knows the only one who can stop his perfect plan is a time leaper.
but he didn't yet mention he's a timeleaper.
and the purpose of him being the dark hero isn't yet revealed.
I can assume kisaki as a child, is living the grey-colored life, where his parents forces him to study, use violences, won't acknowledge if he's not always number one.
Amidst his grey-colored life and boredom, he happens to be stumbled upon a chivalrous kid who hopelessly saved a girl friend in the park, getting all beaten up but still being acknowledged as a hero. From that moment of truth, he pledged to himself "I will become Dark Hero". Thus came the perfect plan to be one.
The scene where Kisaki said "Goodbye, my Hero!" with tears on his eyes to Takemitchy in the future still vibrant in my memory. Just what exactly is Takemitchy to him.