
I knew Kai was hiding his true self from the start. But I still get the feeling Yoshiki isn’t all that bad.

After how he wanted to hit the guy with the stone under the bridge?
Well, I don't think there is anybody in this manga who is a good guy. But probably, that wasn't the intention of the mangaka. They don't have to be good, because they are "bad" people.
And I am curious, where is Yoshiki, what does he know about Kai's plan?

I perfectly understand what you meant. Just remembered the scene with the stone and the fact, that we readers know very little about the characters pasts or personalities. We saw a lot of chapters with the evil? Kai lately but nothing with Yoshiki. Of course, at this moment, you will think Yoshiki is better. Like, when you see an ugly and a cute cat next to each other, you'll pat the cute one not the ugly one. Or if you read a comment, that you misunderstand or don't like, you just say "stupid" and think you did nothing wrong.
I thought I recognized the artstyle. Anyways Higuri Yuu is mostly known for creating Shōnen ai love stories. Hence why there are guys blushing at the other males. So we probably will get the other twin’s romance, but it just won’t be the main focus.