Ryuko is a dragon girl summoned by Yan-Yan’s Sea Dragon Whistle (which resembles Tatsunoko Pro.’s mascot) who doubles as the fourth or fifth member of the Dirt Cheap Trio and as their mecha.

Going with Itadakiman’s “Journey to the West” motif, she is based off Yulong, a shapeshifting sea dragon that serves as Xuanzang’s horse after the former devoured the latter’s previous horse.

Living at the bottom of Otamaga Pond, she is often summoned by Yan-Yan’s Sea Dragon Whistle to either transport the Dirt Cheap Trio across the world or assist with dealing with Itadakiman. To do this, she transforms into a snail like mecha known as the Den-Den Mecha (mistakenly called the Ryuko Mecha in the Royal Revival OVAs).

In this state the Dirt Cheap Trio can ride inside her as she teleports across the world, and with the press of a button can allow the trio to transform a yokai into a giant remote controlled mecha with a mind controlling antenna. She also has a component for several objects including the Divinity Trio gag robots.

Because this is Ryuko transformed into a mecha, there are organic segments such as ribs protruding from the controls and her breasts manifesting as buttons which she does not like being pressed. Any beating taken by the Den-Den Mecha also applies to Ryuko as well, with her being just as bruised up as the Dirt Cheap Trio sometimes.

Occasionally she’ll tag along with the trio on their search for the Divine Puzzle pieces out of sheer curiosity. Though she always assists them, Ryuko doesn’t mind throwing a bit of snark at them or teasing them. She gets along with Kusaku quite well partially because of their mockery of the trio

Beginning with episode 13 Ryuko appears, decked out in baseball attire, on a bullpen cart carrying a small Relief Mecha which she enlarges with her magical breath, and it becomes the main method of the Dirt Cheap Trio’s counterattack for the remainder of the series. One exception was when the trio were slowly turning into trees and immobile, in which case Ryuko launched a giant needle to turn the yoaki into a mecha much like prior instances.

The mechas are still themed after the yoaki creature that Itadakiman has beaten by that point in the episode, and the puzzle piece it had is taken by the mecha to power it. Ryuko keeps watch on the mecha’s generator while the trio control it from the cockpit (which resembles the Den-Den Mecha’s own cockpit).

The spunky dragon girl gets a bit of focus in the sixteenth episode, Ryuko is a Woman Too. In her home beneath Otamanga Pond, she expresses her loneliness to Kusaku while he casually eats her dango treats. While the Dirt Cheap trio explore Italy for the next puzzle piece, she becomes smitten with a gondolier named Wanita . She then tries to get Yan-Yan to relinquish her Sea Dragon Whistle to be with him, but Yan-Yan is also in love with the gondolier and the two star to butt heads.

Unfortunately for both of them Wanita is actually an alligator yoaki enhanced by a Divine Puzzle piece (wani = alligator), which they find out the hard way when they break his guitar during a feud. After all’s said and done and the Dirt Cheap trio is bested again, Yan-Yan and Ryuko are left heartbroken and lonely once more.

(warning: spoilers for Itadakiman below!)

As it turns out, Ryuko does not have any ulterior motives whatsoever and she just kinda disappears after the Dirt Cheap trio are defeated for the last time.

Oddly enough, though the Den-Den Mecha appears in later Time Bokan spinoffs, it never shows any sentience or any indication that it’s Ryuko herself.