Charas who play a supporting role in a story and are not the main characters. They can be part of the main group of charas, but are not the protagonists. And they can be antagonists or on the main antagonist's side, but are never the main villain.
Examples: Erza from Fairy Tail, Shinigami Captains from Bleach, Akatsuki from Naruto for the villanous example (minus Obito).
Charas with an own spin off where they are the MCs do NOT qualify, so Yuuta from JJK or Sinbad from Magi can't be chosen.