Upon reaching the 4th floor of Muscle Tower - a strange, darkened room filled with trees, grass and a pond - Goku is greeted by a flurry of flying kunai and shuriken. The lights turn on and the walls open into windows, letting the sun shine into the room, and the taunting voice of Murasaki congratulates Goku on his victories thus far, but assures him he will go no further. Using lightning quick speed, the ninja darts across the room, using stealth to assault our hero. But thanks to Goku's keen senses (honed by Muten Roshi), he is unable to connect a killing blow.
Listening to his movements, Goku nails Murasaki with a rock mid-jump. Though the ninja quickly scurries away, he drops something important...
"I absolutely cannot allow people who've seen this remain alive!"
"Hey, who were those people?" -Goku
"...Shut up." -Murasaki
And Murasaki disappears once more, taunting Goku from the shadows. "I did make a small mistake, but it won't happen again! This is the ultimate technique of thought! A disappearing technique! Well, kid? I doubt you can find me this time!"
"Aren't you right here?"
"Oh, crap!! I used the wrong pattern!"
(Happy Independence Day, my fellow Americans. ;D)
"You did quite well to see through my camouflage." Murasaki concedes, then promises to show Goku an even higher level of disappearing techniques!!! But first Goku has to cover his eyes and count to 30...
"Hey, what comes after 18 again?"
"No looking during the count!"
After Goku compliments Murasaki on how real his fake boulder looks, Murasaki explains to Goku that he can't expect to keep up when the time comes if he can't count higher than 18! "After 18 comes 19! And then 20!" "Ah! I remember! After 20 is 21, and after that is 22, right? ...and the next one after that is... 23!" "See, you can do it if you try!" Then Murasaki assures Goku that he will now show him the best disappearing technique, if he counts to 30.
30 seconds later, Goku begins to search for the ninja master - and genuinely seems to enjoy doing so. (Even Saiyan kids love Hide-n-seek!) Though he doesn't find him hiding in his house, Goku does uncover an impressive pornography stash hidden beneath Murasaki's floor boards. Then his ears pick up the sound of breathing, which he follows to a nearby pond, a stick of bamboo poking out of the surface...
At this point, a frog leaps onto Murasaki's face, causing him to give away his position.
(This won't be the last time frogs figure heavily into Goku's strategic advantages.)
So Goku pours hot tea into the bamboo, effectively unveiling Murasaki.
Murasaki shouts that he is done using disappearing techniques, and will now be going on the offensive! He encourages Goku to try to keep up with him, as he shows him the speed of the ninja, and begins to sprint away. But this is only a ruse to get Goku to run over makibishi! It works, but only long enough for Goku to run back to Murasaki's house and steal his wooden sandals.
With Goku proving his superior sprinting speed, Murasaki elects to end the fight by showing him the true physical strength of the ninja...
And then Goku shoves his Nyoibo up his butt.
The two duke it out for awhile, sword vs. staff, with Goku having the clear advantage for the duration of the fight. Goku eventually snaps Murasaki's blade in two, and this prompts the ninja to plead for Goku to fight him without weapons... but Murasaki is a sneaky ninja, and when Goku isn't expecting it, he tosses a boomerang-like blade at Goku - which he dodges initially - that comes back to smack Goku hard on the back of the head!!! It knocks Goku out cold, and Murasaki claims himself the victor...