The first Side Story is "Side Story Pack Cirno Arc".
"Team Scarlet Devil Mansion Trial Cirno’s Flight Arc" reveals just how Cirno became a professional Spell Bubbler!

■Outline
Cirno overcomes the trials laid down by Remilia,but can she become a professional Spell Bubbler?!
All will be revealed in this Side Story!

This pack includes the following content.

■New Music
　・Sakkyun Light / Sekkenya
　・Hiiro Gekka, Kyousyou no Zetsu -2017- / EastNewSound
　・Vampire † Kiss / void(IOSYS)
* Songs can be played by clearing the corresponding stages.

■Stages
The side story is broken up into 5 stages where you can battle against different oppnonents.
There’s also Lunatic mode for those who have confidence in their skills!
　・Stage 1 Aya Shameimaru (Wind God Girl)
　・Stage 2 Sakura Izayoi (Sakkyun Light)
　・Stage 3 Patchouli・Knowledge (IMAGINA)
　・Stage 4 Flandre (Hiiro Gekka, Kyousyou no Zetsu -2017-)
　・Stage 5 Remilia・Scarlet (Vampire † Kiss)

More details on the official game page of Side Story Pack Cirno Arc ...