It's implied that Hysterica and Veratos were lovers in the olden time. It's outright when Hysterica is exerting control over Nanami; it looks like a dominant and submissive (and definitely not consenusal).
Vera also had a crush on Lucrezia, her sire and Mina's mom.
Mina's relationship with Yuki is second only to her relationship with Akira (and it just might be a separate-yet-equal thing.) Mina has called Yuki her closest confidante after Akira; meaning that she trusts Yuki more than people she's known her entire life, and just slightly less than the man she loves. Mina has complimented Yuki's good looks on several occasions, and Yuki has been caught openly admiring Mina's adult form. They have begun bathing together and at Yuki's apartment even though Mina is the head-of-state of a foreign power, meaning they are willing to risk an international incident to spend time in the tub together... and yes, there was Skinship Grope involved.