I suppose this was a fitting end when you consider this a personal growth manga, not a romance manga. This was about Yuuki and Mayu returning to normally operating citizens. The full circle served that point nicely enough. In that light Kei and Asuka got disproportionally large roles, making them look like main characters as well. However, when the manga was nearing the end, I'd say they were pushed back to their role as mere supporting characters. If the theme of the manga was healing the wounded Yuuki and Mayu, that also makes sense since Kei and Asuka had nothing to heal. Since it was going to be like that, it's a pity the author felt the need to pair up Kei and Asuka. If Kei had turned down Asuka, it would have granted an opportunity to further show Mayu's growth by having her console Asuka. It would have underlined this is a personal growth manga, not a romance manga.
All in all, a decent manga. Thank you, ElPsyKongroo, for bringing this to us translated!