Why did she kill him?

When the main dude went to see Hana, the boy said he would slit his throat. (Not sure why)

Later we see the boy and the girl following the main dude, then run away.

In part 1 her grandfather says he she went back even though he cut her hair off.

Anyways, what was the reason for killing the dude's BROTHER instead of the dude himself?

I hope there's a good explanation not just "to facilitate the plot twists".



~ Observe, and act with clarity. ~