Alright today the Mothra grub went into its cocoon almost as soon as it woke up and turned into Fairy Mothra about an hour later, it started at weighing 30 tons, but when I played the minigame with it I noticed that its weight went down even further from 30 so I kept playing (tapping the middle button with the Tama in my pocket while working.) and found that the lowest weight for Fairy Mothra is 1 Ton! I think that's the lowest weight for any of the characters on the Mothra Tamagotchi, although that's still pretty heavy compared to Fairy Mothra in the movies where it's only slightly larger than the two Shobijin Fairies because it carries them around and can fit in a human's hands, here is the example.
Also even though I never disciplined Mothra as she went through the Larva stages, Fairy Mothra's justice meter was halfway full as soon as it hatched, so if it attacks any buildings I'll go ahead and discipline her because I'm hoping for the secret character.
Also while the Mothra and Battra grubs and all other adults eat their food in two bites, Fairy Mothra is like the baby and larva stages, taking three bites to eat her food, which is an Apple.
Here are her stats right now.
Age: 8 days
Weight: 1 tons (The lowest possible, it won't go down to 0.)
Hunger: 4/4 Full
Happiness: 4/4 Full
Justice: Halfway Full
I might make a picture for it, but the problem is that in the movies it is basically just a resized Mothra for the Shobijin to ride around on, so I would have to make up a different color scheme for it, and it also only has two wings in the Tamagotchi sprite like a Fly, whereas in the movies it has four wings like Mothra or Battra (Although I guess technically those are just two large wings split into two sections each.) so I'm not sure what I'll do, and I haven't seen if it sleeps with a blanket yet either.