First of all, he won the Blade Dance when he was thirteen. There is a reason "Ren Ashbell" is called the Strongest Blade Dancer.
His fight with Jio is all kinds of awesome. The two of them are in the middle of a cave, and begin using three-dimensional combat techniques to jump all over the place like Spiderman on drugs.
Fighting and defeating Velsaria, who is known as the strongest elementalist of Areshia Academy, with a giant hole in his chest.
Kamito generally has a one-on-one battle with the opposing ace of an enemy team, which get increasingly epic (and destructive) as the series continues.
Any time he dual wields Est and Restia, infinite amounts of badass is unleashed.
Muir is a super-assassin who can control spirits that are physically impossible for humans to control. She has never defeated Kamito.
In volume 9 chapter 7 part 1, Kamito jumps and stands onto Ellis's Ray Hawk that had been embedded into the ground. Ellis uses a wind power so that Kamito SURFS ON HER ELEMENTAL WAFFE THAT HAS BEEN SHOT FROM THE GROUND INTO THE AIR towards a giant spirit flame demon summoned by Muir. He then JUMPS OFF RIGHT ABOVE IT and UNLEASHES BURSTING BLOSSOM SPIRAL BLADE DANCE EIGHTEEN CONSECUTIVE STRIKES.
After Restia sends Kamito into a HBSOD, she saves him from a rampaging spirit and wakes him up with a kiss.
Her strategies have saved Team Scarlet from defeat more than once.
Unlocking Scarlet's true name allows her to single handedly wipe out an entire team of elementalists, including one who gave Kamito as Ren a hard time.
She is able to fight off Rubia's Mind Rape and turn the situation against her by awakening Kamito from his Demon King Form.
Rinslet
Her reasons for being in Raven class, which is comprised of gifted problem children. Claire is there because of Rubia. Rinslet is there because she went full-on Mama Bear on anyone who mocked or bullied Claire in front of her.
