In arcade mode, meeting specific conditions will allow you to face a secret boss after the cut-scene for defeating the final boss ends. Each character's secret boss is Mu-12 Unlimited, except for Mu-12 herself who instead fights Ragna Unlimited:
Encounter secret boss Mu-12 Complete arcade mode with any character (except Noel) with at least three Astral Finishes and without getting knocked out once.
Encounter secret boss Ragna Complete arcade mode with Mu-12 with at least three Astral Finishes and without getting knocked out once.
Unlock the following medals at the "Gallery" menu by performing the corresponding tasks:
MEDAL - HOW TO UNLOCK All You Need Is Love - Don't buy any items when starting Abyss. Don't Get Cocky, Kid! - Earn one victory. Fatality - Land more than 30 Fatal Counters. Ice-Ten - Using Jin, freeze your opponent more than 10 times in a match. It'll Only Hurt for a Minute - Crush your opponent's guard. Level One...! - Watch 'Previously On' and 'Opening' in Story Mode. Other Fish In The Sea - Use over 9 characters. We Have to Go Deeper - Defeat the boss on Depth 300 in Abyss. Welcome to the Abyss Hole - Defeat the boss on Depth 100 in Abyss. Who's Got Next? - Complete Arcade Mode. I Get Around - Use all characters. Wait, You Mean There's More? - Earn a victory in Score Attack mode.
How do you complete Ragna's story?
It's at 88% and don't know what to do.
Answer from SovereignDeity
There are 3 endings for Ragna. The good ending where you win all fights, the comedy ending with the ghosts, and the bad ending. When you fight against Rachel, lose intentionally. You will then continue the story. Just win the next fight for the bad ending