I never know how to feel about Saikawa. In one moment, he seems sweet and supporting which I love, but then in the next moment he has thoughts like "I don't want him to show his face to anyone else", "I don't want him to expand his social circle", "I hate seeing him having fun and chatting with other people". Seeing Sayama opening up to other people and becoming more confident is something that I personally love to see and is one of the reasons I actually like this manga. So to see Saikawa (who is supposed to be his biggest supporter and someone who LOVES him) just get upset about his progress just comes across as douch-ey and insecure. But at least he's trying to support him despite these thoughts, and he don't really say them out loud, so at the same time I can't completely get mad at him. He also did say that Sayama mends his insecurities which is positive. But I dislike how this manga seem to romanticize this aspect about Saikawa, when it really isn't something positive at all. I wish he would focus on feeling happy for Sayama rather than getting insecure about him widening his horizons. That would be great character development for him as well. But eh, I think I like him more than dislike.
Other than that I liked this a lot more than I expected. I really like Sayama as a character!!