Essence of Purity
From Essence of Purity:
At 23, Nagamori Kasumi is the new employee of a model agency but his cute face makes him look much younger than his real age. The most famous Japanese model, Nishimuro Shiki, works at the same agency… He is the so called Cinderella Boy. But he is in fact an 18 year old kid with a pretty harsh personality who drives all of his assistants away one after the other. Having enough of his constant whims, the manager tells him to choose up his own assistant. And Shiki decides to pick Kasumi.