“EX(Extra) Rumia” (EXルーミア, Ekusutora Rūmia) is an old Touhou Project fan theory suggesting that Rumia has a sealed extra boss form, building on Rumia having an ofuda ribbon on her head that she can't remove herself and has never been explained or expanded upon.

In the Touhou Koumakan omake file, we are first told that Rumia's ribbon is an ofuda that she cannot remove, and that's all we had for an entire decade. It was finally revisited in Volume 3 of Strange Creators of Outer World, adding that nobody knows how it got there, then her Dai Touhouten¹⁾ plaque hints that it was contained 'secrets within' that have yet to be brought up in any of the official media.

The character has no official design because it's a fan theory after all, so people are free to speculate on what happens to the ofuda ribbon (e.g. float, halo, disappears), what happens to her hair length, whether she has accessories (e.g. jet black wings, large black cross, large black sword),²⁾ and whether it 'ages' her body or not. Once again, this is all common fan interpretations.

• It has yet to be discovered when people began to speculate about the existence of EX Rumia, which seems to fall between 2002 and 2005, given the theory's implied familiarity by 2005.³⁾
• The theory would inspire numerous copycats, since it's easy to understand that 'EX' is Extra Stage and 'PH' is Phantasm Stage,⁴⁾ bringing us EX Letty, EX Cirno, EX Wriggle, and so forth.

• The Legend of Twilight - As a secret final boss.
• Touhou Igyoukyou
• Touhou Youreimu (“Osana Reimu”)

• EX Rumia on the Niconico Encyclopedia
• EX Rumia on the Pixiv Encyclopedia