Hey

There's Kekkei Gekkai and Kekkei Totta, which both belongs to Blood Limit but they are different attributes.
Mei would fall under Kekkei Totta

As for Ao, I'll look into it. But I'm pretty sure he would also fall under it.

Question, why does Mei fall under Kekkei Totta when in the anime and manga, the only known Kekkei Totta is Onoki's?
Technically Ao and Mei should both be Kekkei Genkai, otherwise they would buff more than just two elements.

No, Mei does not have Kekkei Touta she has 2 Kekkei Genkais.

how about part of pain, they have rinegan unit ? what its just dojutsu, if i remember rinegan is come after mangekkyo sharingan

actually mei have 3 attribute, but they just write it water and fire xp missing wind/earth atribute (im forget)

Ya Mei has 2 Kekkei Genkai.
1. Youton no Jutsu (Earth + Fire)
2. Koumo no Jutsu (Fire + Water)
As far as i know she never use Kekkei Touta even though she has 3 elements. Dunno about Ao.

Yes she has 3 elements but never use kekkei touta.

Exactly, having the ability to use 3 elements doesn't automatically mean they can perform a Kekkei Touta.

Kekkei Genkai is the ability to combine 2 elements in one jutsu, a feat not just any ninja can do.
In Mei's case she is actually proficient with 4 elements, Earth, Fire, Water and Lightning and out of those 4, she can do 2 combinations, Lava Style and Boil Style (translated as Vapor Style in this game).

Ao has seal status, so his Kekkei Genkai is not buffed, as it is not released in this form i guess

Mei know's Kekkei Genkai even though she knows 3 styles: water style, earth style, and fire style.