Mars+ is a character that appeared in chapter 1 act 3. He messaged Ryann under the username anotherVenus+.
He was so far only seen on page 284. He looks similar to Mars except his hair is shoulder length, he has a red symbol on his left cheek and his hair and clothes are stringy like Sari's. He's using a yellow laptop and an ominous bipedal silhouette can be seen behind him for a split second.