The tune is also very catchy, and the translated lyrics are... creepy.
"Memories of Phantasm", despite the pretty girl designs, is actually nothing but a "Bullet Hell" game series. Which has one of the most frighteningly devoted followings of anything I've ever seen. The game does have some backstory and real character designs... from which one fan, or group of fans, created their own anime openings and even a couple of full-length anime episodes!
I can't even draw crude sketches of my own characters. I can't imagine what it takes to do stuff like that, even with modern programs to help.