In order to unlock this, you need to clear The 4th Survivor mode.
(And in order to unlock the 4th Survivor mode, you need to beat the 2nd Run mode with either character and see the true ending.)
Mechanically identical to the 4th survivor mode, except all your voice-lines are cute japanese voices at different pitches and you aren't fully decked out in elite gear.

The Tofu Survivor is equipped with only 16 half durability knives, 2 green, 1 red, and 1 blue herbs. The gauntlet you go through is the same as with the 4th Survivor Mode

Manage to beat The Tofu Survivor, and you'll get a nice surprise.....

Your surprise is 2 more new blocks of fun!
Konjac & Uiro-Mochi

Conjac is the no-nonsense fire and explosive expert.
They carry an upgraded Chemical Flamethrower, an upgraded Grenade Launcher,
6 grenades, 1 green herb, a first-aid spray, 1600 flamer fuel, and 40 flame rounds.

Uiro-Mochi decided that Conjac's 6 grenades were an insult to destruction itself.
So they brought ALL of them (36 to be exact)
Clear a run with either of these 2 and you'll unlock the last 2 tofu squad members...

Flan & Annin Tofu are the unique weapons specialists that get the job done in their own special way.


Flan took the phrase Go Big or Go Home to heart
with their massive Minigun, Anti-Tank Rockets, and Spark Shotgun to take on any tyrant.
(with 200 more ammo for the spark gun and 2 flashbangs as well)

Annin Tofu took her fast gunslinging to Raccoon City
with their Quickdraw Army and M19 Pistol and a whole lotta herbs (9 green, 1 blue, 1 red)
They can win any firefight. The extra 360 shots can't hurt their chances.

You may ask what the amazing reward is for completing all these challenges with each Tofu squad member.

Your reward...... is a model for each Tofu character you clear the mode with (as far as I know). So you too can see the amazing animations that went into this eclectic cast!
Since this is a joke mode, I wasn't expecting anything too amazing as it might be unfair to those who can't dedicate the amount it takes to do all these runs.

I'm unaware if there is another secret for completing each character in a certain amount of time. I will update this if indeed I discover there is.