How do I beat this?

Hmm! The promotion exam is a crucial crossroads in a Nyan-ko's life! Among the Ultra Rare cats you own, Black Cat and Black Miko are very powerful against elemental enemies, so be sure to include them. I hope you pass smoothly with a solid combination!

How much treasure have you collected so far?

I recommend collecting up to Future Chapter 3 of Treasures before attempting. For Ultra Rare units, Black A. Bahamut, Chronos, and Amaterasu should be enough to clear it.

If you're really struggling, try gathering 2 Gwangmuts and Hackers, then add Aphrodite and Heukruno. You should be able to clear it.

From my experience, it's easy if you max out all treasures for Chapter 3 of the Future arc. Just maxing out the Alien treasures makes it easy.