These are the lines the two exchange while fighting after Yoo-hyun enters the spiritual realm.

A brother who, without relying on items or equipment, possessed the same fire resistance as I did and held black flames in his hands. Though he was my only blood relative, we were different in so many ways—yet at this very moment, he felt like the only kindred spirit, the only one of my own kind, in the world.

A dark, blue blaze—just the two of them—where no one else can set foot.

The S-Rankers I Raised

I think this is the episode that best shows just how much Yoo-hyun loves Yoo-jin ㅠ No one else sees Yoo-hyun as one of their own, and even to others, Yoo-hyun is far from what you’d call human—but the fact that she says she only sees her brother as one of her own is so touching. Also, everyone tries to come between Yoo-jin and Yoo-hyunBut Yerin promised Yoo-hyun she’d create a future where he could be with Yoo-jin, and I absolutely love the moment when Yoo-jin and Yoo-hyun trust Yerin and enter the spiritual realm without a care in the world ㅠ