It's a (power) fantasy and often an attempt at Slice-of-Life, usually with battle-waifus. Most harems go to shit because they're very same faced and predictable in both the MC and the girls. To repost my old rant.
this thread reminds me why most harem shows, other than DxD are annoying. All this over-sexualization for no reason except anime-gags. At least DxD doesn't try and hide behind the whole 'pure protagonist' bullshit the others do and instead revels in this.
There are very few Harem anime that are good or fun, such as Ranma 1/2 or is Zero no Tsukaima (though in the end Saito subverts the usual harem stuff by having Saito leave with Louise for his world after marrying her and her alone, though in his case you actually wish they had gone all the way with the harem route)
Let's list off the number of SHITTY Harems, starting with the ones I can think off the top my head:
- Testament of Sister Devil (or whatever its called) is DxD if written by an edgy fanfic writer who doesn't understand what DxD is about, (I actually plan on writing a comparison on the two later).
- Unlimited Fafnir, a weird as fuck typical anime similar to Black Bullet except unironically having the main character getting intimate with the 'dragon lolis'. It's less a cohesive story and more a mixed bag of story ideas from other better anime like Evangelion
- Girly Air Force is like Dragonaut but as a (potential) harem and with the reasoning for the protagonist actually being there in the first place as rather weak. It's also a wierd attempt to fetishize planes
- Rosario and Vampire, initially has a cool idea but doesn't think about the long-term and makes the vampire too over-powered and edgy while the protag is bland and weak.
- In another world with my Smartphone: It's OP done wrong, simple as that. It's got no stakes, not even the shitty, SAO-type ones.
A good video got made on this actually; How to (Not) Handle an OP Character - Ft. Isekai Smartphone: https://www.youtube.com/watch?v=wz3dBaUh9PUPost too long. Click here to view the full text.