The Job Change menu in Mary Skelter: Nightmares
Jobs (職業, Shokugyō) can be obtained with Job Rights by reaching a certain level and purchased with the required Blood Crystals. When you change a Blood Maiden's Job they retain the same level, but stats are changed to the job that you've chosen for her. Various skills are available to each job and can be viewed via "Skill Creation".
The different job styles
As noted by Mary Skelter 2, there are different job styles that each character fits into that defines the jobs they can have. There is the Magician Style, featuring Thumbelina, Little Mermaid, and Hameln in Mary Skelter: Nightmares, Fighter Style, featuring Alice, Cinderella, and Hameln in Mary Skelter 2, Science Style, featuring Snow White, Gretel, and Charlotte, Libero Style, featuring Red Riding Hood, Rapunzel, and Mary, and Archer Style, featuring Sleeping Beauty and Kaguya. Otsuu is an exception to the rule, as she can have different jobs that fit into each of the styles.
Starting in Mary Skelter 2, some spells require Chants. This means that the character will prepare the spell when selected and cast it on their next turn.
Magician-Style[]
The jobs that focus primarily on skills, with high SP, TEC, and MEN. It is a set of jobs useable by Thumbelina, Hameln in the first game, and Little Mermaid.
Fighter-Style[]
The jobs that specialize in front-line combat, with high ATK, HP, DEF, and/or AGI. It is a set of jobs useable by Alice, Hameln in the second game, and Cinderella.
Science-Style[]
The jobs that are more utility-based compared to others. Along with stat changes between them, each job has some kind of gimmick that alters gameplay. It is a set of jobs useable by Snow White and Gretel, and some of the jobs are useable by Charlotte.
Libero-Style[]
Libero-Style jobs are generally well-rounded jobs with the ability to fit into any hole in a group, whether that be physical or magical damage, buffs, or debuffs. It is the set of jobs useable by Red Riding Hood, Rapunzel, and Mary.
Archer-Style[]
Archer-Style jobs are suited to back-line combat, having high AGI and ATK with low DEF. They have access to long-range weapons and skills that allow for multiple hits in one turn. They are useable by Sleeping Beauty and Kaguya.
Altair-Style[]
Altair-Style jobs can help fill out whatever the team needed, as each job is a sort of fusion of every job from each style. As such, she can manage to have many differing stat-lines. They are only usable by Otsuu.
Executioner-Style[]
Similar to Altair-Style jobs, Executioner-Style jobs can fill out whatever niche that a team needs. This comes with different skills and stat lines with each different job. They are only useable by Pyre.
Sleuth-Style[]
These jobs are very similar to Libero-Style jobs. They can only be used by Mary.
Minstrel-Style[]
These jobs are either borrowed from Scientist-Style jobs or very similar to that style of job. They can only be used by Charlotte.
DLC Jobs[]
These jobs are available for purchase or free download with the games. They can be restricted to certain characters and are generally not as good as the base game jobs, but they have some good skills and unique aesthetics to them.