As Susuki said, there is no honor in fighting. Kou fought dirty in Hokkaido, and the same principle applies here. "It's your fault for leaving an opening."
What I really dislike is that the manga seems to be coming to an end and we got almost nothing from Akira and Hatsuka. What was the point of portraying Akira as lonely, even within her own family? What was the point of showing a brief flashback of Hatsuka in a female school uniform when neither...