The Rude Hero: the enemy.
No entry in Monster bestiary.
"Wait, he's definitely not his normal self!"
Keep all of your players's HP high because Yuri and his fusion, Death Emperor can do a lot of damage to your party. Have Keith attack the Yuri with his physical attacks while Zhuzhen is using his special skills and healing if necessary. Alice should mainly heal the party and use Blessed Light when not healing. Also Alice should cast Holy Edge on Keith will make Keith physically attack with light effectively against the dark-type Yuri. Equiping the Warlock Earrings on Zhuzhen is a risky but effective stragety as the sage is focused on casting Special Skills. Once Yuri's HP is at a certain level he will transform into Death Emperor, the fused monster will attack with physical attacks and his special, Dark Messager.