Second "s" in names that ends with the s

Question

Well, it's one particular name from One-Punch Man, Genos. Sometimes i see it's written as Geno's arm/body parts or something along the line, but not the Genos's arm/body parts. Where did second s go?

Answer 1

The character's name is Genos.

The possessive of Genos can be Genos' or Genos's, which is a matter of style. However, Geno's is an error, as it would require that his actual name be Geno - which it is not.