Those are Ctenanthe amagris, which are supposed to be very hard to grow from what I’ve heard.

The mother plant also grew this fast, so I made a few cuttings to propagate her.

That’s how she looks now:

I can’t stop them from flowering…

The only issue so far has been that I’ve simultaneously both over-fertilized AND let them run dry while having extremely low air humidity because I forgot to close the window a while ago. This resulted in all existing tips burning, but this hasn’t happened yet again on the new growth.