Iroha Tamaki was fighting witches while her technical younger sister Nemu Hiiragi was watching her Nemu was a friend of Iroha’s younger sister Ui and Nemu referred to Iroha as “Big sis Iroha.” and she was a magical girl but wanted to watch her and the witch was going to attack Iroha until Nemu yelled.

“Big sis Iroha lets go now..”

Iroha then jumps where Nemu was on grabbed Nemu and then left the witch and Iroha was on the floor still in magical girl form and was looking for Nemu.

“Big sis..”

Iroha then runs to Nemu and holds her and Nemu gives her a grief seed.

“Don’t cry please big sis..”

Nemu grabbed Iroha’s arm.

“If I become a witch I’ll keep you safe big sis Iroha..”

Nemu then uses her magic which forced Iroha to transform back into her school uniform and Iroha holds Nemu.

“Hold onto me Big sis Iroha..”

Nemu’s soul gem darkened and then the area changed around them and Iroha got dizzy and passed out and Nemu then turned into a witch named Pennen Nenemu and then Iroha was in the labyrinth on a bed similar to Iroha’s own and she woke up on it.