Ken Murata

Murata is Yuuri's former classmate. He often gets into trouble such as having delinquents picking up a fight with him. He's actually a happy-go-lucky type of guy that sometimes hit on girls, bleached his hair, getting over-friendly with Yuuri's mom, and he often stumbles upon Yuuri's house just to eat her curry. In the first season, after the incident with the time and space being unstable, Murata accidentally (or maybe purposefully?) drops by into the other world with Yuuri. He's already suspicious since the beginning because he easily speaks the same language as the villagers. He's even more suspicious when he spoke to Yozak like he knows everything going on and planning the best possible way.

Soon after that, it's finally revealed that Murata is actually the reincarnation of the once Great Sage (or Daikenja) of Shin Makoku 4000 years ago. His place was to guide Yuuri as King to regain the four forbidden boxes and defeat Soushu (which that time remained in Shinou's soul). In the end, he succeeded and Yuuri managed to did it, even though in order to make that plan successfully work, Murata had to 'pretend' to betray Yuuri and the others. Murata is more like a babysitter figure towards Shinou, because of the time they had spent together in the past, and him being Shinou's most trusted strategist.

Even so, he truly respects Shinou as a leader and even when he (Daikenja, 4000 years ago)'s dead and reincarnated into a different person, all he thinks about is how to defeat Soushu. As the Great Sage, he is really bright and wise. He acts calm and never rushes to do anything. He relies on his brain and strategies. His power cannot stand alone, but he can amplify the Maou's power, and has lent Yuuri his powers when he needed it. Murata is a really mysterious person, he usually hides his pain and past just to himself.