Mars-san

Mars-san (A.K.A. Tasei-san or The Martian) is a non-NPC character found underground on Mars.

He is a tall, indigo creature with a single large eye and a single foot. He is found weeping near what appears to be a crashed locomotive.

Interaction
Mars-san produces a remorseful three-tone chime when Madotsuki interacts with him, coupled with a small darkening of the screen. Additionally, he can be stabbed with the knife effect. This will not kill him, but leaves a wound on his foot and changes the color of his eye from red to green, and a second stabbing will change his eye color back to red.

Trivia

 * Some fans consider the creature that is sometimes seen in the pond on The Witch's Island to be the son of Mars-san due to its likeness to him.
 * Mars-san is a significant character and a large source of speculation. He is included in most theories about the game.