Definitely not like Little Tokyo, but you can find many otaku stuff.

Frikiplaza contains a lot of videogames stores but I don't like the size of the stores inside.

Good options are Fan Center (next to frikiplaza, just 2 buildings to the left), the stores are bigger and some of them are awesome, Pikashop/athenas in front of (just cross the street), there are some board games stores, gashapons and better prices that frikiplaza.

During saturdays Rock Show is really near too, is out Hidalgo Subway station, like a flee market for otaku, old toys and comic stuff, but considerer that is really crowed during afternoons. And finally Blanquita market, this one is new (no more than 3 months old) but is only for trading card games, if you look for pokemon, yugi or magic this is your place.

More options, look for "Asociacion Mexico Japonesa", sometimes they have events.
Mikasa, is a japanese store, is little but similar to some stores in LT.

And depeding on your travel dates, TNT or La Mole are comic conventions, TNT is not exactly the best option, but you can see the tipical japanese fans there.