Both Nagi Kirishima and Rayne are often associated with a striking red and black color scheme in their character designs.

This shared visual element, while perhaps coincidental, could contribute to an immediate visual recognition or even a sense of visual harmony (or perhaps even a subtle visual contrast depending on the specific shades and how they're used) if they were to appear together.

It's another layer that could make their interaction visually appealing and thematically resonant, further emphasizing the "blood" aspect inherent to both their characters.