My Personal School Flower

An average high school student, after shadowing an elderly man who asserted he was the world's greatest assassin, picked up kung fu skills and unexpectedly obtained a bottle of elixir, granting him various abilities, leading him down a path of no return. What is this? Am I seeking revenge against this old man? What? A stunning and alluring beauty sharing the same apartment, a stylish and captivating police flower? Well, for the sake of my purity, I’ll go for it!