Kouya and Madarao - S1.E11

It's another night of Kekkaishi duty. Yoshimori encounters three minor ayakashi, Honetarou, Uhosuke, and Nagao, and easily captures them. However, Madarao's old companion, Kouya, shows up and in anger attacks everyone, including his followers. After a brief flashback of Ginro (Madarao) and Kouya's happy past gone wrong at the hands of the humans, Kouya gains power from Karasumori and transforms. Yoshimori releases the seal on Madarao revealing his real form. Madarao and Kouya then battle.