In some slice-of-life shows, just like in real life, good things come to those who wait. Hopefully.
Rainbow Days features 12-minute long episodes, but with the show confirmed for 2-cour, we will be getting about the same amount of content as a full-length, one-cour show. Which is good, because a show like this definitely wants a decent amount of time to work its magic. As a shoujo slice-of-life show, it works on a slightly different aesthetic than most slice-of-life, which is aimed at a male audience. It features at its core a group of four guys, and the interactions among the four definitely is a notable part, but there is also some romance involved, as the first episode revolves around the crush one guy, Natsuki, develops on a girl-and right after he was dumped by his previous girlfriend, too! (She was just passing out tissues for the karaoke place she works at.) I'm normally somewhat against rebound relationships, but it's a high school slice-of-life, and those sorts of emotions aren't exactly uncommon, so I can roll with it.
The girl in question, Anna, is very stoic and emotionless throughout the episode, so we don't know too much about her, though she does wear the muffler that Natsuki gave her during their first encounter. (Then again, maybe she just lacked a good muffler.) We do know that, for reasons, she frequently naps in the room of a teacher that happens to be one of the other guys's older brother, something that gives Natsuki some imaginative ideas on what sort of relationship the two have, and not to good effect for him. While I doubt there is anything really going on between the teacher and Anna, the episode nevertheless ends on an inconclusive note in that matter, though with perhaps the first step toward the two actually having some kind of meaningful connection.
Slice-of-life shows with a significant romance element come up from time to time, and like most romances, they have to be given some time to build up to be meaningful. This is especially true in a slice-of-life romance, where you often do not have the luxury of using forced drama to push a relationship forward, only the feeling that, day by day, the two of you are getting closer. (Although said build-up does not have to all happen before a romantic relationship starts, as last year's My Love Story showed quite well). As such, on the romance side, I'm definitely expecting a bit of a waiting game, to see just how things develop. Not only that, but the OP and ED suggest that each of the other guys will get their own girl to form a relationship with.
That said, just waiting for a relationship to build up is not that interesting, so there needs to be something in the here and now in the show to appeal to viewers in the meantime, and that takes the form of the interactions among the four main guys. The friendship between them can definitely be seen, in the form of how much crap they casually give each other. Obviously, they all care about each other, but what's a group of friends without some good old-fashioned ribbing? Though even here, things are set to get better later on, as right now the interactions are mainly the other three guys giving Natsuki a hard time over his crush; once other girls start interesting the other guys, expect the guys to give each other hard times in all directions. That's always good for a laugh.
This show definitely is letting things build up for now, but it's doing a fine job of it, and I'm looking forward to how things will develop in later episodes.