Split it into two sheets for Meisters and Weapons
Meister
Name:
Nickname:
Age:
Gender:
Class:
Appearance:
Abilities:
Backstory:
Weapon
Name:
Nickname:
Age:
Gender:
Class:
Appearance:
Weapon Form:
Special Abilities:
Backstory:
...Something like that. Class would be either EAT/Especially Advanced Talent (Soul Eater) or NOT/Normally Overcome Target (Soul Eater NOT), Abilities for Meisters would be stuff like Soul Menace or special traits, everything else is easily explained.
As for a plot... Soul Eater 1964 I got no serious ideas at the moment.