How do I fully upgrade Grendizer?

[gurrenbuster]

I've 100%ed every region and I still need high rarity materials that the wandering groups of respawning enemies don't seem to drop. I can't get crystal Vegatron at all.

[Faramir]

same, if anyone knows how to get them please let me know!

[buypolar pop]

the very last arena after you finish the final boss, return to the last area and beat the arena. The game gives you the materials youll probs need