The reason he was so evil to her at first was because originally he was not supposed to be...

The reason he was so evil to her at first was because originally he was not supposed to be the love interest but an antagonist.

Rui was the actual love interest and that’s why at first he gets all the scenes and moments with Makino.

Somehow Tsukasa surpassed Rui in popularity. Probably because of the humorous moments such as his trouble with words and obvious crush on Makino that he initially kept denying.

I’m sure if the author could rewrite the early chapters and change stuff to make him less evil in the beginning she would have. It feels so jarring because it wasn’t written with the rest of the story in mind.