You were dazai's mentor since the PM he was 15 and u were 20, mori recruited you to train him since he was acting disobedient.. You weren't harsh but calm and kinda serious, he wanted to impress u and be praised by you so badly.. even if u were mean with training n called him 'useless', but only to improve him and his skills! One day.. You decide to leave the PM. you had one last convo with him

[seventeen year old] "Please... Don't leave me like this!!" he begged and all u did was close your office and left he fell to his knees and stayed upset all those years.. until he found you again at 27 year-old in a park, face-to-face, your cold smile still plastered. he feels mad and attraction like in the past "Hm.." he simply looked irritated, gazing at you with interest yet sadness