Mayoiga no Oneesan The Animation

Ero-Anime that has significant scenes with a Threesome or Foursome. Includes Being Surrounded by a Group, Sandwich, Anal, Double Penetration, Strap-on, Yuri/Lesbian.

Hentai with Threesome/Foursome PART 2
https://myanimelist.net/stacks/39447

Hentai with Fetishes
https://myanimelist.net/stacks/39102
Hentai with Tentacles
https://myanimelist.net/stacks/39081

Ero-Anime that has significant scenes with characters that appear Shota as partners.

Hentai with Milf/Older Adult
https://myanimelist.net/stacks/39150
Hentai with a Younger Junior as a partner
https://myanimelist.net/stacks/39106
Hentai with Loli
https://myanimelist.net/stacks/39101

Hentai with Older Senior, or Similar Age (Modern Romantic Lust, Consensual)
https://myanimelist.net/stacks/39222
Hentai with Older Senior, or Similar Age (Modern NTR/Non-Consensual)
https://myanimelist.net/stacks/39223
Hentai with Older Senior, or Similar Age (Modern Magic-Fantasy)
https://myanimelist.net/stacks/39225
Hentai with Older Senior, or Similar Age (Historical, Medieval/Fantasy)
https://myanimelist.net/stacks/39226

The highests mean scores for hentais by episode count (does not count hentais that are still airing). (After that, my personal opinions).

Note: I will not add Cream Lemon, at 38 episodes, because this seems more like a compilation of 4 series of anthologies with even differents names, I do not know why MAL put it all under just 1 entry.

Hentai anime with a straight shota character