A series done by Sweet Little Neko (https://www.deviantart.com/sweetlittlenekochan).
1. Annabeth Chase
3. Thalia Grace
5. Rachel Elizabeth Dare, Lavinia Asimov & Reyna Ramírez-Arellano
7. Sally Jackson
9. Hazel Levesque
11. Juniper, a chryseae celedon & Kinzie
13. Sadie Kane
15. Hestia
17. Sarah Jacobi, Jasmine Anderson & Medea
19. Athena

https://e-hentai.org/g/2380259 /5b5e81e81e/

Base +5, S.Skygazer -8, Bigfeet69 -7

I can't believe there's more than one "Percy Jackson and the Olympians" gallery.

Base +16, Eden of Shirock +6

Multiple book series and a couple movies, I'm kind of surprised that there are only 13 galleries with the tag.

Base +21