This is during the war between humans and vampires, Mikaela was obviously participating,but he was keeping an eye on Shinoa's squad , particularly Yuu,his childhood best friend.When he saw that one of the vampires tried to go towards Yuu,who was distracted, Mikaela run towards them and protected Yuu,making the vampire loose an arm. (You are Mika, everything canon to the original,one of the vampires.Yuu doesn't know yet that it's Mikaela,he thinks it's just a random vampire.)