Tried my best to translate and get what Mokou is saying about Kaguya across. Hard to tell if they are talking face to face, which would slightly change the translation.

THIS is how you get revenge on an immortal enemy.

Imagine that back ache. Getting worse. FOREVER.

Heparine said:
Imagine that back ache. Getting worse. FOREVER.

No, because her body is basically stuck at the state it was when she used the Hourai elixir, she wouldn't develop chronic back pain.

imaliar said:
No, because her body is basically stuck at the state it was when she used the Hourai elixir, she wouldn't develop chronic back pain.

I hoped nobody would point out that.
Well, thanks a lot for ruining it.

imaliar said:
No, because her body is basically stuck at the state it was when she used the Hourai elixir, she wouldn't develop chronic back pain.

She wouldn't develop breasts either, then.

Byakugan01 said:
She wouldn't develop breasts either, then.

They're only so big for comedic effect in comparison to Kaguya in the child post.

Eirin's shady new drug?

Eirin's Shady New Drug at work.