Benefactor

Yato was Kazuma's benefactor, and Kazuma wasn't one to leave a debt unpaid. For years, he watched Yato, looking for an opportunity to repay him - he never found one, but he watched as Yato's first mask, his first defense, broke, and then watched some more as Yato created a new one. And in between, he saw Yato, real and so, so tired.