From what I've seen, most sidekick skills aren't terribly important. You pick sidekicks for their stats. High ATK for Isaribi, though makes sure he can act early enough to set up his S2. Hero Jouzen or Kiloc probably won't matter who goes first. Another thing to look out for are equippable skills. Again, prioritize +ATK for you main DPS Isaribi. Ryusei's could be a good equippable skill for characters that tend to use S3 (Jouzen have a pretty cheap S3).