Now we are getting dark.

Rumia is the first boss of EoSD. She is a youkai that manipulates darkness. Sounds pretty scary right?
Her problem is though that she is sealed by a talisman in her hair that she cannot remove. This symbolizes how humans have grown less afraid of the dark thanks to electric lights.

But happens if that talisman is removed?
Many Speculate that removing it will reveal her true power as a human eating youkai. She would then turn into a form commonly known as Ex Rumia (Ex as in Extra(Extra as in Extra stage(Extra stage as in post story stage that features a ridiculously hard boss(Ridiculous hard as in not as hard as Phantasm, but harder than stage 6 boss)))).

But even with the sealing she is dangerous as her darkness ability aids many other youkai in their hunt. If she were a RPG character, I would make her a support for youkai that love darkness (like Mystia Lorelei)

Rumia also has this pose that looks like humanity started using the decimal system.