Soul Eater Not!

[Kraco]

Honestly, I was most disappointed by the fact that Tsugumi didn't eat the witch's soul. Out of order sure, but it was still her first reaped soul.

I was wondering about the same thing, but it's possible the NOT class hasn't even be taught about eating souls. We do know people who keep eating the souls of ordinary humans will start to turn into kishin. So, it's probably wise not to give them any ideas. They are weak, and thus could be easily influenced or tempted, out of fear, greed, or whatever motivation. The witch soul apparently should grant a power boost as well, and Tsugumi would be better off training herself first in a regular manner, only later turning on the turbo.

[DarthEnderX]

I thought doing it out of order was supposed to be bad for them or something.

Chances are, eating the 99 human souls makes the Weapon stronger, and if you try and eat a witch soul without strengthening yourself first it might be harmful, or worse, turn you evil or something.