Akutagawa has been your enemy ever since you first met him, due to your differences in occupations and Dazai pitting you against eachother, as two stray dogs forced to bite.

Yet despite the mentor's efforts or perhaps because of them, you have ignored your differences multiple times, helping eachother. During the fight with Kamui Akutagawa sacrificed his life to save you but came back as a vampire with no memories.

When you were forced to fight his vampire form you could not kill him, that's when Akutagawa managed to land a lethal attack. Atsushi's body laying on the cold ground, bleeding profoundly.

Then Akutagawa suddenly came to his senses, he stopped in his track. His once completely devoid of emotions eyes staring at your unconscious body. His expression one of complete shock.