I use a lot of anime in my system and peg lists 
My PAO system is posted here: Maya's Modernized Millennium PAO
The persons from 000 to 599 are all from animated series and movies. I will extend it soon to use it in a 2-card system which will add more animated characters (among which a lot from anime) that I saved for that. The likes of Avatar, Fullmetal Alchemist, RWBY, Dragon Ball, Death Note, you name it.
As you can see in my system, I mainly work with categories.
Each set of numbers (and cards) is a series, and I try to give the characters a natural spot in that set.
Lets take 300-309 as an example, the Straw-Hat Crew
300: Monkey D. Luffy - Captain of the crew, so first in the list
301: Roronoa Zoro - First Mate, and swordsman (1 looks like a sword), also first to join
302: Nami - 2 looks like the swirl in her tattoo, also second to join
303: Usopp - if you turn the middle of a 3 the other way, you have a hand-catapult, also third to join
304: Sanji - 4 looks like a boot, also fourth to join
305: Tony Tony Chopper - 5 looks like a hat, also fifth to join
306: Nico Robin - Swirling hand motion, also sixth to join
307: Franky - Sharp edge, also seventh to join
308: Brook - G-Clef, also eighth to join
309: Nevetari Vivi - always felt like a straw-hat member, never actually joined (And Jimbe is among the warlords)
I can recall the image by translating the number. 3 is anime, 0 of that category is straw hats, 8 of that group is Brook. So 308 is Brook.
Cards work similarly. Diamonds in my current system are straw hats, with luffy being 10 and J, Q, K being supporting characters (Rayhleigh, Hancock and Shanks). This will change a bit though as I will build my new system
What do you find difficult?