Hmmm... we may need some clues on this one Chionos.

Is it significant that the first line is repeated twice?

It's definitely a reference to "An eye for an eye, a tooth for a tooth" but the way Chionos has written it is clearly a lot more one-sided. "Some teeth for an eye" implies that there are many deaths in revenge for one death or vice versa.

The last two lines remind of those Tamagotchi pets that were all the rage a few years ago....

I've no idea but I'm gonna have a wild guess with White Materia?