Megaman Xtreme 2 - Getting "The Real Ultimate Buster"

Not my discovery, I found this out from a helpful GameFAQs guide, specifically this one: https://gamefaqs.gamespot.com/gbc/478... I think this was a request as well, though it's been so long since it was asked that I've forgotten who asked it and where. Anyway, here's how you get The Real Ultimate Buster for X. Music is from Castlevania Chronicles, which is a modified PS1 release of Akumajō Dracula on the Sharp X68000.