Taking levels in monster types

Today I found this post on reddit and in one of the comments they mention taking levels in fey, outsider, and aberration (not all at the same time). Are there any alternate rules I’m not aware of or are they just referring to monsters as pcs rules from the srd.

Heres the OP

Over the past few days with some help from members of the /r/touhou Skype group, I have made a spreadsheet listing (almost) every Touhou character and have filled in some slots slots along their names accounting for their D&D Morality Alignment, Four Temperaments, MBTI, and other silly things that aren’t as relevant.

Chart (not very complete): https://docs.google.com/spreadsheets/d/18l9L-jEret6eKSXMA-51nC9jwPYfAODp3ogKUgXiyZo/edit?usp=sharing

D&D Alignments explained: https://en.wikipedia.org/wiki/Alignment_(Dungeons_%26_Dragons)

Four Temperaments explained: https://en.wikipedia.org/wiki/Four_temperaments

MBTI is harder to grasp, especially the cognitive functions but there are more than enough online resources detailing that.

Enneagram explained: https://en.wikipedia.org/wiki/Enneagram_of_Personality

If there is anything that should be put in or whatnot, please leave your thoughts on characters and also your alignment/MBTI/other if you like.

EDIT: If I like a suggestion and want to add it, I’ll do so in the name of the user who suggested it. You can also leave comments on the sheet as well.

Here’s an excerpt

Now, let’s see. You’ve given D&D (presumably 3.5e rather than 4e or 5e) classes and Pathfinder classes as a category. I can definitely help with that. Going down the line:

Rumia probably doesn’t have class levels, but she’d be a Commoner or just take levels of Outsider(Edit: Or Aberration, depending on how you see Youkai) if she did.

Letty Whiterock is probably just a Fey.

Kogasa Tatara is just an Aberration with Aberration levels.