Those are Yumehara Kazuya x Kitagiri Yuusei and Lucan X Ryuuhei. I felt like these pairings were kind of similar.
Though Lucan is a demon and sadistic he really cares only for his ally cat King, his childhood-friend Kubinashi and his love Ryuuhei. Kazuya and him are both oblivious to other feelings and desires towards them. I guess Kazuya is more of the friendly side, sometimes maybe bit innocent?
As for Ryuuhei and Yuusei: they´re both quite quiet, read a lot, observe others and are protective without openly showing it. They have their own principles they live after(? Sorry if that is wrong). Both are intelligent and are tricky. All of them love cats.