@BananowyJE But that's not Melfina's true body. It's an artificial construct that her mind and a portion of her power can use. So he hasn't really summoned her yet.
But yeah, you're right that since the fight with the very rapey mind controlling wannabe protagonist, there hasn't been much relationship development between Kelvin and any of the girls in the manga. Perhaps further into this arc we'll see something, or perhaps not.
@Scrabbleman I sorta forget that Rion is a girl sometimes to be honest. She's a huge tomboy battle junkie who takes after her "nii-chan" after all.