Foe Yay: The official Ronin/Warlord rivalries are sources. The rivalry between Anubis/Shuten and Ryo breaks the mold, but takes the Foe Yay to the next level. Rowan and Kayura definitely had their moments of this too.
Rowen: It looks like I'm falling for you, Kayura!
Kayura: You know I'll only break your heart!
- It doesn't help that both of their voice actors share the same last name (possibly married?).