Kento had heard enough. He was not going to let Rihito take advantage of Mei. Sure, Mei had her faults – she was tomboyish and loud and half the time won their fights – but she was still his friend and the girl that he liked… okay, a bit… and he wouldn't do anything dishonest like Rihito wanted to do.
Mei had been dazzled by Rihito's manners – and Kento had to admit, they were impeccable – and she wasn't thinking clearly. She was too innocent even as she was a pain and he couldn't let Rhito and Mei's grandfather do this to her. She was only thirteen! Rihito was older! Rihito should know better than to sleep with an innocent thirteen year old.
But apparently Rihito didn't, so Kento had to protect Mei. Protect Mei from her grandfather and her oh-so-perfect butler, and everybody else that would take advantage of her. Because he wanted to protect Mei's innocence, and Mei's self, and any other part of Mei that Rihito and Mei's grandfather wanted to touch.
And he wasn't in love with Mei. Not at all.