Though the tag is harem, I wonder if it’s the typical harem where all the girls like him or the type of harem where he’s just surrounded by girls? So far Iruna is the only one other than Lefi who might like him, but she’s too young so she’s out of the question. So I doubt this is a traditional romcom harem, it’s just feels more familial than romantic. Which is really nice, hopefully it stays like this because Yuki and Lefi’s relationship is flirtatious but not to the point where they are officially together, it’s a nice change of pace. They enjoy each other’s company, especially far into the future where both of them would be thousands of years old. So all in all, it’s a charming relationship which isn’t very common in manga I’ve read.