The short answer is you since you get to name the protagonist. Shin Megami Tensei IV is set in East Mikado, a country that draws from medieval Europe, but has samurai instead of knights. Shin Megami Tensei IV takes place in 1492 where East Mikado is protected by walls that cover that perimeter. Higher walls in the center of the city shield the castle and King Ahaziah Mikado.
Famitsu explains the protagonist is an 18-year-old male. He has a revelation in a dream that his choices will shape the world. When he wakes up he completes the Gauntlet Ritual and becomes a samurai. In Shin Megami Tensei IV, samurai hunt demons in secret. Only a few people know demons exist.
Issachar (left) is your childhood friend and kind of acts like a big brother. He wanted to become a samurai his entire life and is with the protagonist during the Gauntlet Ritual. Hope (right) is the leader of the samurai. He guides initiates like the protagonist and puts protecting the nation above everything else.
While your mission is to exterminate demons, Shin Megami Tensei IV gives players demon allies too. You can fuse demons and talk with them. Below, on the right, Nekomata is asking the protagonist to show his feelings. It looks like Atlus redesigned some demons for Shin Megami Tensei IV. Yomotsu-Shikome looks different compared to her Shin Megami Tensei: Nocturne design.