Anbu : Anbu have no fixed rank. They can be anything from a Chunnin (elites among Chunnin) to an Elite Jounin.
Elite Chunin : Not a canon rank. Will be given to elites among chunins in this fanfic.
Special Jounins : They are Elite Chunins that have one skill at Jounin level.
Jutsu ranking levels :
Rank E - Academy level
Rank C, B - Chunin level
Rank A - Jounin level
Rank S - Elite Jounin level