In a mysterious unnamed kingdom (Dragon Ball filler, why don't you ever name these places?), the gate into the Demon World has been opened. And Princess Misa has been kidnapped...!!
We join Goku heading south, along the path chosen to train for the next Tenka-ichi Budokai. Along the road, he meets a kindly old woman who feeds him, and tells him he ought to pick a new direction to head in. "See that castle over yonder?" She says. "At its base, lies a village of demons! Why, just last night the princess was kidnapped, and now everyone is in a panic! Rumor has it that when night falls, monsters come out from the Demon World Gate to cause havoc!"
"Hey! Anyone here?"
(Goku can't just stay away then there's strong guys to fight.)
The (human) village at the base of the castle erupts into booby-traps once Goku arrives. Goku overcomes the minor obstacles easily, growing frustrated at the villagers' obstinance. Finally, an old man reveals himself, surprised by Goku's strength. He takes Goku to the castle, and offers him to the King.
The old man explains that Goku is as strong, no, stronger than any of the monsters from Demon World -- and could possibly defeat their leader!! The King of Demons!
...No... not that king of demons.
...not him either.
The OTHER King of Demons!
...God damn it, Dragon Ball.
Shura. King of Demon World*.
The (human) King tries to talk Goku out of it, telling him that the Demon World is full of horrifying monsters and demons that will capture and kill him. "Then I just won't let them capture me!" Goku says cheerfully.
"Oh ho ho ho! How ignorant!"
"Oh ho ho ho! What's ignorant mean?"
The King commands his guards to throw the foolish boy out... so Goku beats the crap out of them.
The King, his men, and Goku arrive at the Demon World Gate. Propped open by a sword, planted as a challenge by Shura, that will only come out if he is defeated by a human (or a saiyan...). So into the Demon World Goku goes!
Gora and Mela, two demon guardians, block the way.
The Guardians of Demon World ask Goku if he has a permit from Enma-sama and Kami-sama to pass into the world of demons. When Goku says no, they attack! Goku beats them back fairly easily, when Mela seems to be struck with an idea. Discovering Goku is out to defeat Shura, she gladly takes him to his realm; where he is holding a wedding between himself and Princess Misa! (and of course, Goku has no idea what a wedding is...)
And what wedding would be complete without a martial arts tournament???
And so Goku competes in MORTAL KOMBAT.
Though Shura's strength is far greater than Son Goku's, he manages to exploit the Demon King(-ish)'s weakness against light! Using a Kamehameha, he makes an opening so he can pound Shura into submission, then grabs Princess Misa, puts her on his back, and runs for it! Gora and Mela guard the way back to the human world, and Goku gets Misa back to her father, the King. Finally, Goku pulls out the sword, and the Demon World Gate is once more shut!
"Looks like only the gods of death who have the key can come and go now." Mela says.
Shura remarks, "Damn that boy. He certainly showed me up."
"Being hurt once in awhile is good medicine, don't you think?" Mela smirks.
Shura smiles back, and together, with Gora, they return to the feast.
Mela promises to see Goku again some day... but hopefully not too soon.
*in this filler episode anyway.
Some thoughts: Something interesting about this episode is that it uses a lot of designs (specifically, the demons) and music from Sleeping Princess in the Devil's Castle. It also feels like a much more compelling version of that story. I really enjoy this filler episode (if you can't tell by all the shots I took and that I'm taking time to say so.)... anyway, onward Tenshinhan Saga!