Like the other commenters have said — this story left a lot unexplained. In favor of a quite long and unnecessary last arc. Though, I do think Rokudou and Ranna had a lot of sweet moments together, throughout the series. The two had both rocky and lovey-dovey times, which I think is all that's needed for a good romantic resolution to a story like this one. Overall, slightly weak towards the end, but still a good finish.
Still, lots of loose ends left unresolved:
1. Rokudou's parents being the most absent parents in the world. It's not like our boy's an orphan. He mentions that he can get money from them to go on the hot springs trip. But we never see even their faces once. Let alone know their names. Let alone hear them speak even one sentence to Rokudou. I want to just headcanon that Rokudou's an orphan, but the story does mention his parents existing — so, sucks. But, these kinds of absent parents are still a very common cliche even in anime and manga today. They've been a thing in anime since God knows when.
2. I guess the whole supernatural element of the story? For one — why was Ranna born with so much malice? Is she a demon reincarnated? Or is she just fucking evil, for no reason? Then there's Rokudou's magic. Honestly, the supernatural stuff being left unexplained isn't that big of a deal to me, though. Sometimes, not everything needs to be explained. I don't think super intense worldbuilding or lore drops are necessary for an ultimately lighthearted coming-of-age type of story that this manga is.
I like that Ranna's violent nature wasn't completely erased. People don't change that easily. I like her character arc just the way it is. If, before, she was 100% malice — then now she's more or less 50/50 after meeting Rokudou. More importantly, she can control her violence now. Notice how she doesn't directly strike the bad girls running after Rokudou here. Instead, she just blocks the path, haha.
The three things I liked the most about this manga are:
1. Rokudou's growth as a protagonist. Definitely not your reader-insert bland harem protagonist. Dude is super manly, has some real balls.
2. The supporting cast's constant presence throughout the story, and how they feel so real. Colonel and Kachou are the types of "fellow loser friends" that get forgotten by the story once the MC changes and finds new friends in most anime — but these two stay relevant the entire way through. And they're not dislikable, either. The same can go for the other characters. Iinuma is a bully-turned-buddy archetype done extremely well, one of my favorite characters in the story. The other villains that come back as friends later on are likable too.
3. The subversion of Rokudou's harem. They're only his harem girls by a technicality. Eventually, each of the heroines grow out of their crush fro him as they become better people — and find other guys more suited for them.
Minami and Nagori, Osanada and Kurokata (say what you want about this one, but Osanada's never cried in front of Rokudou after she stopped liking him — whereas she cried like a baby to Kurokata in the last arc), Ling Lan and Tateshima (sharing a cigarette), and obviously Azami and Aoi. Oh, Yashiya and Yagen, too.
The girls aren't treated like inanimate prizes for Rokudou to show off his status as a super ladies' man. Raino gets a clear answer without being led on as well. I think Chiyo's more focused on her relationship with her mom than boys after she "grows out of the crush".
All's well that ends well, overall. Rokudou got the girl of his dreams, without exploiting his magic. This ending does feel very open on purpose, like there might be a sequel. Who knows.