"Apparently, Hell used to be an underworld, but they moved. We did some concerts in the former Hell, which is just a big underground party city for oni now."

She hands over an advertisement card touting "HORISMRIVER".

"I'm Horikawa Raiko, come to our concert tomorrow, I'll duel you now if you want but if you just showed up here it feels unsporting."

"Interesting, I wouldn't have expected that it was just the depth they were referring to. I'm not quite sure what you mean by duel so yeah that might not be the best idea. I wouldn't know what sort of attacks to use and I also wouldn't want to misjudge one of yours and get sent back home. Who knows if I could find this place again."

"Ostensibly, people can't enter or leave this place easily. I can, that might just be a fake thing people tell themselves. I go to concerts outside all the time. Do you know, there's this one band with three drummers, all in the front of the stage? That's the respect we deserve."

She shrugs. "I'm not good at dueling rules but you just sorta end up following them unless you specifically try not to. Maybe it's magic or something? The main specific thing is declaring your spells beforehand, I guess, but that's mostly just about how many rounds you go for, so there's a win condition. Some people are nerds about all of it, I'm not."

"That sounds like it would be a strange experience, I don't really have names for most of my attacks."

"I was like ten minutes old and pretty addled the first time I did it so I feel like it's pretty intuitive. To be clear, it's not a duel if you're clearing out the ambient fairies on your flight path or something. There's some kind of minimum bar for...uh, sapience, I guess?"

"I wonder if I would be forced to play along but even if I'm not that sounds fun enough to do regardless."

"It's a fun form of self-expression, even for us musicians. After all, we can go up against someone with our playing."

"Were you controlling the lightning storm earlier then? I wasn't sure."

"That's right. There's a bit of thunder god in me ever since I seized divinity. I think I was shaped right to follow Raijin's groove, in a manner of speaking."

"I think I'd like to try this duel thing then. If you're interested.

"Sure."

Raiko smiles. She declares three spells.

(This just feels like an ontologically simple action, though if one cares to be skeptical about this one can decompose it into a complicated interaction with ambient magical fields, but not to the extent of divining what the spells might be. It's easy enough to do without any practice; the world wants you to do it.)

"Three for three, and I'll give you the default if we each run out?"

Okay, she reaches into her magic and decides her three spells will be:
The hammers of justice
The questing hearts of unrequited love
And The curse of the wyvern.

"That works for me"

She switches to combat form, a number of red hearts appear swirling around her not precisely obscuring her but sketching out a boundary of where her shield now exists.

Raiko takes to the air as one of her bandmates starts playing again, filling the space between them with some largely pro-forma bullet patterns, large widely spaced V-shapes.

She's holding her first spell at the ready, and she'll start drumming with her band too. She's not moving around too much, mostly just hovering.

The band aren't particularly playing instruments; they have instruments, but they're just directly making sound by magic. (The violinist is making electric guitar sounds.)

Raiko is drumming for real, though. She looks pretty happy, but focused.

She'll dash towards Raiko in the air and when she gets close unleash outward spiralling hammers.

Now that they're both in motion, it's time for her to use her first spell, while seeking out gaps between the hammers through which to slip.

三鼓Third Drum「午前零時Midnightの'sスリーthreeストライクstrikes」. A simple pattern; three summoned drums each shotgun bullets chaotically into the air, bobbing and rotating. Watching for fire from three directions at once may be challenging, but it's predictable enough.

The gaps between hammers are practically non-existent but Akira has to pause briefly before each of the three times she sends them out which should be enough time to get clear. 

Akira... is not well suited to such tight gaps with her shield fully extended so she pulls it in allowing her to dodge going forward.