To help me deal with my When Will Tenso Finish Registering My Packages anxiety, I've finally found a good song to use Rikka in! It really highlights her soft, almost sultry lows. The only issue will be getting her vocals to cut through the instrumental... I'll run a mixing test after work, and if it goes well I'll post a snippet to share here.
The OG is a duet, but a semi-popular cover of it turned it into a solo, so I'm also debating whether to throw Maki in there or not. The thing is, Renraku Madaa pushed Saki's lows; this song absolutely slaughters them. So if I get her involved I'd have to find a balance between making her audible and making her, well, palatable.