Just a head's up, since we talk about eroges so much on the site, we decided to affiliate with MangaGamer. Despite that, you can expect only honest discussions here. That's a given since we'd only cover stuff we actually like. Anyway, on with the sweet yuri love.
The A Kiss For the Petals series is nothing but yuri as far as I can tell. I played one other game besides this one: A Kiss For the Petals - The New Generation, and it was great. I recommend that game too. There is twincest in there. It's an overarching story that covers a single period of time from different perspectives. You can follow one couple and briefly run into another couple. Then when you follow that couple, you'll see the first couple again. It's terrific writing. But we're talking about Maidens of Michael here. Maybe we'll talk The New Generation another time.
As said, there's no 'main character' or 'main couple', since everyone the player follows is the main character in their own equally important story. While it seems like the plot of Risa and Miya being set up as a couple at the spur of the moment, despite not actually dating at the time would be more interesting than anything else, that it would be the inciting incident that gets the plot moving, don't skip the other couples. That's just their story, and there are other stories that will definitely hook you.
The real inciting incident is the school event 'St. Michael's Best Couples' where an informal poll was cast, and the best couples were chosen by the students. These couples, Risa + Miya, Yuuna + Nanami, Sara + Kaede, Reo + Mai, and Eris + Shizuki are tasked with working together to plan upcoming events. These couples are not copy-pastes of one another, the girls are all unique and well fleshed-out. Just a heads up though, Sara and Kaede both have the last name Kitajima, they are cousins. I know that's not to everyone's taste, so there's your heads up.
There's something of a sequel to this game titled A Kiss For The Petals: Remembering How We Met that follows Risa and Miya, taking place after Maidens of Michael. It's brief, but the story is nice and it's well worth the cheap price.
All said, if you're a fan of yuri like I am, the Kiss for Petals series should be well on your radar. It's all yuri and there's no darker elements to mess it up.