Puella Magi Holy Quintet is the name for a group of five magical girls in Mahou Shoujo Madoka Magika and it consists of:
They’re seen in the original anime during the 10th Episode and they later appear during the Rebellion movie. They can also be found in Madoka Magica spinoffs. The magical girls formed their group when Homura transferred to their school and decided to become a magical girl.
Mami is mostly shown as the leader of the group as she seems to be the oldest and the most experienced magical girl of them all. Honestly, they’re all pretty cool and make a strong and effective team for eliminating Nightmares.
Sometimes they can be seen with Momoe Nagisa, and sometimes with Aki Mabayu (where they appear in Puella Magi Madoka Magica: Scene 0)
