Kinnosuke Kashao (火車王 金之介 Kashao Kinnosuke?) is the only son and the seventh in line of the Kashao School of Martial Arts, which specializes in not spending a single yen and passing on all their bills to others. Due to this lifestyle Kinnosuke lives in a cardboard box in the park, although he imagines it to be much grander than it really is.
"Kin" is "a small quantity of gold" or "10,000 yen", referring to his lack of money, while "suke" means "assistance". When read Kashao can mean "King of Borrowing", referring to his talent for getting other people to pay for him. However the kanji used to write the name mean "King of Flaming Chariot". "Flaming Chariot" is a Japanese idiom meaning "having difficulty making ends meet" or "one's estate suffers".
After seeing Nabiki Tendo's skills of avoiding paying a bill, Kinnosuke sends her a challenge letter. Initially Nabiki uses Ranma Saotome's female form as a double for her. However, when she sees Kinnosuke she sends Ranma flying so she can have him to herself. After enjoying a meal together the waiter comes over and asks if they'll be paying with credit card, to which Kinnosuke says he'll call his assistant.
April then appears who, after being asked to bring the credit card, says he forgot it to which Kinnosuke says there's no helping him now. Kinnosuke says that this is quite embarrassing, to which Nabiki ponders what they'll do now as she never brings her purse on a date. Hearing this Kinnosuke says that she amazes him and tells her he really wants to go out with her (meanwhile, the bill gets sent to Ranma and Akane Tendo who had come to supervise who the challenger was).
The date continues with Kinnosuke and Nabiki going to a clothing store and Nabiki selects out several outfits, while Kinnosuke picks out a suit (which April says was made for him). However, when the shop attendants ask if he'll be paying for them he says he has to use the restroom first. Nabiki quickly tricks Ranma into having to pay for the clothes before sneaking round the back of the store and asks where they'll go next.
Kinnosuke and Nabiki decide that the next thing they should do is rent a whole theme park for themselves. That night Kinnosuke asks Nabiki if he'll see her again, to which Nabiki replies that of course he will. As Nabiki learns that Kinnosuke sent all the bills to the Tendo Dojo, Kinnosuke himself tells April that he lost todays battle to which April asks Kinnosuke what he means. Kinnosuke explains that although the bills were sent to the Tendo Dojo, Nabiki herself didn't spend a single Yen, so he decides that in the next date he'll make her use all her money.
The dawn of the next date arrives and Kinnosuke is awoken by April. Kinnosuke goes to brush his teeth, revealing that he's actually sleeping in a box in the local park, he then continues saying that Nabiki is the only woman not to fall prey to him and he'll make sure that today she spends her money. When Kinnosuke arrives at the Tendo Dojo he enters using a Helicopter as several bills for the expenses (Kinnosuke's suit, the flowers and rental of the helicopter) fall down from the sky.
Nabiki then arrives, wearing a new elegant dress (much to the despair of the near bankrupt Soun), she tells Kinnosuke that for today's date there'll also be a bet of whoever spends ¥10 today will have to pay for all the bills on the date, including those from the previous date. Kinnosuke accepts the bet and tries to make Nabiki spend it almost immediately by getting a large group of young girls to ask Nabiki for donations.
As Nabiki is in Kinnosuke's helicopter which he rented she has nowhere to run and she can't possibly turn her back to cute little girls. Luckily, Ranma and Akane were told by Soun to watch over Nabiki and they each give the girls ¥100. Nabiki then tells one of the girls to put ¥10 on the dish of a box and when the girl does a small clockwork bird appears and takes the ¥10. The other girls think this is cool so begin doing the same, meanwhile Kinnosuke looks on in surprise that Nabiki is actually making money.
Kinnosuke decides to use another ¥10 ploy and suggests they go for something to eat, and after protests by Akane and Ranma not to make it too extravagant they settle on getting Ramen. However, the four of them end up flying to Hong Kong where they order Shark fin Ramen. The group then proceed to a Casino where, as Ranma has to work as a Bunny girl tells Nabiki not to get into too much debt.Unfortunately for Ranma the debt ends up being a hundred million Yen and both Nabiki and Kinnosuke leave Ranma and Akane to send the bill.
Later on and back in the Helicopter, Nabiki decides she'd like to go somewhere and sing some Karaoke. It turns out that they rented the whole of the Tokyo Dome to sing the Karaoke (much to the disbelief of Ranma and Akane). Afterwards the four go into a hotel and rent the Royal Suite. When Ranma tells Nabiki she's a High-School student and should act like one, Nabiki agrees but acts more like she's in grade-school and begins to draw graffiti with Kinnosuke as well as ruin and break several items in the Royal Suite.
While Nabiki talks to Ranma and Akane, Kinnosuke asks April what the bill is and he says it's ¥5 million for the both of them. Kinnosuke decides that it's time to finish Nabiki off and the four of them get a boat ride on an expensive cruiser home. April begins to talk to Nabiki, while Kinnosuke asks what they're talking about and says he doesn't like being left out. April takes Kinnosuke and explains to him that Nabiki has feelings for him, which now Kinnosuke realises he can't believe he didn't notice sooner.
The two are then at a fountain and Nabiki tells Kinnosuke that if ¥10 is thrown in there love wll blossom. She then takes out ¥10, but Ranma in a panic breaks the fountain. Nabiki tells Kinnosuke that he needs to give her a ring as evidence of his love and Kinnosuke is about to spend ¥10, but finds the ring from a Drink Can and uses it instead. The four return to the Helicopter which is carrying what Kinnosuke says are wedding gifts for Nabiki (Ranma notes that the debt is now at ¥500 million, to be corrected that they're actually at ¥1 billion).
As Ranma recovers from this shock, Kinnosuke grabs a parachute and jumps out the helicopter. Ranma shouts angrily at Kinnosuke he can't leave in the middle of a ¥1 billion fight, to which Kinnosuke tells them to look in the cockpit, revealing that it takes ¥10 to operate the helicopter (which began falling when Kinnosuke left). April asks Kinnosuke if he did really like Nabiki, to which Kinnosuke becomes slightly teary eyed and tells April he's in the middle of training right now. Kinnosuke then opens his parachute, but it turns out to be a fake replaced by Nabiki.
After talking about how much she loves him, Nabiki (who jumped from the helicopter with Ranma and Akane) offers Kinnosuke a parachute at the price of ¥10. However, Kinnosuke refuses and falls to the ground. Nabiki and April tend to Kinnosuke, who tells Nabiki to call his personal physician and hands her the number. April then gives Nabiki ¥10 to make the phone call as Kinnosuke's life is at stake. Luckily for Kinnosuke, Nabiki phones the emergency services instead which doesn't cost anything to phone.
Nabiki then goes to Kinnosuke and tells him they need to split up and holds Kinnosuke's ¥10 in front of him. She then tells Kinnosuke she'll keep this as consolation, meaning the Kinnosuke lost the challenge. Kinnosuke goes to the hospital, but gets out of paying all the bills by escaping out through window of the Hospital room he was in.
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With April: April is Kinnosuke's loyal puppet butler. Kinnosuke takes April on his hand everywhere he goes. April acts like a old butler concerned about his young master. While April would seem to be just a puppet, he sometimes does things without his masters approval such as borrowing money to phone the hospital for Kinnosuke. This could mean that either Kinnosuke suffers from a split personality or has relaid to April so much that subconsciously he has given April his own "life".