Honestly, I'm wondering why people here don't really understand why is Mai even back here again in DOA6...
Don't misunderstand, I get when people don't want her back because they feel it's a disservice to the other past DLC characters(
@DestructionBomb), But I also feel some didn't really understand the very reason and the point.
Mai Shiranui is back because of 2 very important reasons(Get heads out of the gutter):
1) SNK's contract with Team Ninja/Koei Tecmo did not expire unlike how it did with Virtua Fighter(which is potentially the reason they didn't return or have new VF characters taking over instead.
2) Mai was either popular enough for SNK to allow her back and/or she must have also been successful enough for SNK to add in ANOTHER character on top of that.
This was obviously a business decision that TN/KT and SNK both reached a consensus on and I wouldn't be surprised if SNK felt that making Mai a guest on DOA was the right decision for them enough that they wanted her back in and added another character on top of it(they could have very well refused to continue it and let the collab die).
In terms of pure business, this must have been a massive success for them to even do this, thus why Mai is the very rare guest from a different franchise altogether to make an immediate return to the next game.