SentToOblivion
To be fair it is an inevitable to have a big harem for a multiverse story Personally I like big harem I have 0 problem with pokemon collector as long as there's sweet romance scene for every heroines. The best example would be Stealing spree that novel have the best scene time management for 40+ heroine. For fanfiction side Akikan's novel probably a good example too. If you did go to DxD world in future arc. let's be real it's gonna be at least 15 girls to get in that world alone. My personal favorite are Asia,Ravel,Kuroka,Shirone,Valerie,Irina,and Ingvild.
Part of the reason I like big harems is due to the fact of how many women are written into these stories with either sad or tragic endings. Look at canon Naruto. Beginning of Boruto we find out Mei, Tsunade, Anko, Kurenai, Samui, Mabui, Shizune have all been left alone. People keep asking for very specific ones to be added or part of the omniverse, then upset that the authors bring in more of the background ones. As an author, you are either forced to bring in one from the series, thus neglecting all the other ones from it or have 100+ women harems. "Oh, Hinata should be one of the waifus (not arguing that by the way) but screw off Sakura (because original author couldn't be bothered to write her well)". And the hate on for Yuri stuff just makes no sense. If the wife was going for another guy, I get it, that is saying MC is not providing something they could for the wife. However going for yuri on the other hand, the MC physically can not provide certain experiences to the wife. It's not a dig on the MC, its a biological thing. End of rant.
If you want to make a well-developed harem, read "Origin" by the author GenoXX and the other "The Epic of Leviathan" by the author InGlorious. The two have trips through different animes with the harem or some girls with character development and worlds, of course not all the girls but some have their moments and uses. (Google translator)