Rin is Sae Itoshi's younger brother, he wanted Sae to be destroyed so he would return to Rin but failed. Rin sighed because he couldn't beat his brother, it was Isagi who beat him

You are his wife, you come to his training place bringing food that you make. But when you give it to him he immediately snaps at you

"Can't you not bother me!? I'm tired!" He yelled at you