Nyudō Mifūne (三船 入道 Mifūne Nyudō) is the behind-the-scene coach who guides players with unconventional tennis. He is as tame as a ferocious pet. He is known as the Drunken Coach.
Mifūne Nyudō appears as the hidden coach at the U-17 camp, training on the top of a mountain.
He is a very skilled coach, able to transform and evolve the losing middle schoolers through strange tasks he forces them to perform on the mountain. Coach Nyudō is also able to withstand the Inui Juice (type: Special Vegetable Juice) Echizen Ryoma, Oshitari Kenya, and Tanishi Kei snuck into his sake bottle during the "Special Mission."
The Drunken Coach wears an attire similar to Echizen Nanjirō. He appears to be old in age and has long dark hair. His body is very hairy as well.
He is almost always seen with a bottle of sake.
He never hesitates to curse or insult a player around, nor is he hesitent in hitting a player.
He is also very fond of alcohol- forcing a set of "random" students to sneak into camp every year to steal sake from the bar lounge in the main camp, though there was training secretly incorporated with the assistance of Coach Saitō.
Though he appears as a harsh and possibly heartless coach, he seems to care about his students. While implied to the middle schoolers that their jerseys were buried in a hole after he peed in it, it is later shown that he is still in possession of them with no harm done on the jerseys. He later sends these same jerseys back to the middle schoolers prior to the Genius 10 challenge.
Two Years Prior To The Storyline
It is unknown when, but during this time, Byōdōin Hōō went to train in the Mountains with the Drunken Coach.
One Year Prior To The Storyline
It is unknown when, but during this time, Tokugawa Kazuya went to train in the Mountains with the Drunken Coach.
The Drunken Coach is introduced as the coach on top of a mountain on the U-17 grounds that coach Saitō had the middle school losers climb up,
The 27 eliminated middle schoolers climb a mountain only to find the eliminated high schoolers from the start of the series. The Coach instructs the middle schoolers to perform weird tasks that include: digging a large hole for him to urinate in, sleeping in a cave, training during midnight while it's raining, jogging through the forest against the high schoolers while chased by eagles, and instructing Ryoma, Kei, and Kenya to steal sake from the main camp... while running through lasers.
His strange tasks are not in vain though - the eliminated middle schoolers realized their improved techniques (Ryoma and Kintarō can hit 5 balls, Kenya has better balance and improved speed, Sakata can run in zig zags, Gakuto can do a low moonsault, Sanada has a larger and stronger black aura, Kei lost weight, etc.)
When the Drunken Coach notices Ryoma and Kintaro's improvement he tells them they are still a long way from Tokugawa and Oni who can actually hit up to 10 at once. Ryoma asks the coach arrogantly to teach him how, to which the Coach furiously hits him across the face. In retaliation Ryoma gets up and serves a conker past the Coach's face on purpose stunning the Drunken Coach. To this, the Coach ends the exercise.
After Sanada organizes the middle schoolers and high schoolers to steal the Coach's sake, the Coach gets angry to the point he decides they should all go back to the camp and start a revolution. Upon returning to the camp, it is unknown which of the 24 middle schoolers, but some of them defeat the 2nd Court which angers other High Schoolers seeing them return. They quickly handle the High Schoolers with a problem with their return and the Coaches announce they are the new 2nd Court.
Sometime later, the Drunken Coach is seen by a fire next the jersey's of the middle schooler's hanging on a string- showing that he did not actually burry the middle schooler's jerseys in the hole with his pee. He comments on how those fallen middle schoolers will change the world.
Genius 10 Challenge
The night prior to the Genius 10 Challenge, Coach Nyudō sends the jerseys he had taken from the middle schoolers back to them. The jerseys were neatly folded within a large box and then dropped off at the official U-17 Training Camp by airplane. The box would then land in one of the tennis courts before Oni, who then returns the jerseys to the middle schoolers. It is unknown if he was the person who piloted the airplane.
After the G10 matches were completed, he was revealed to be the head coach of the U-17 camp.
- Hobbies: Bullying scums (useless people), drinking
- Favorite color: None
- Favorite food: Meat, Alcohol
- Most wanted thing at the moment: Alcohol
- Thing that he is bad at/Dislikes: Electronic goods
- Specialty other than tennis: Raising eagles, training
- The eagles that appeared during the sportsman hunt were carefully raised by Mifune from the time they were still eaglets. 
- If Mifūne Nyudō is found to have been the pilot of the airplane that dropped off the middle schooler's jerseys, it may be assumed that he was also the person who had dumped the 300 tennis balls at the training on the day of the middle schoolers' arrival.