Mahouka Koukou no Rettousei

Do it, then you will understand.

 Spoiler

Tatsuya's "badass" persona is entirely made up in the viewer's own mind, he legitimately has no emotions, he's just a puppet whose only goals in life are to support his sister (who is from an important family, he's basically programmed to be her slave). You merely think he is cool when in reality he is nothing, he is not even capable of making decisions for himself, his only point of reference on whether or not he is doing something correctly is his sister's reaction.

 Spoiler

He wasn't stripped of all emotions. He was stripped of the strongest emotions, except with regard to his sister's wellbeing. In other words, he is perfectly capable of hating a person if that person is a threat to his sister. He also likes to tease people every now and then because he finds it amusing (most of which the anime cut out). If he was completely emotionless, he wouldn't do that.

He can make decisions for himself. He's done so multiple times. If his sister wasn't there to push him into joining the competition, he wouldn't have. In fact, he was ready to get the hell out of there before they pulled him into it, but his objection was overruled by his sister.