The Nebula Cup Arc is the first anime-only story arc in Mouretsu Pirates and the shortest arc in the series. The yacht club enter a dinghy tournament, however they are unaware of the emnity that arose due to Hakuoh's actions a few years ago, or a group who is targeting Marika.
Not long after returning from pirating with the yacht club, Marika is continuing to work hard despite being very tired. Around the same time, Grunhilde is feeling a little uncomfortable with how close her sister has become with Marika. The yacht club make a trip up to the relay station in order to carry out cleaning and maintenance on the Odette II, after which Marika goes to the Bentenmaru to do some cleaning by herself, using her ID ring. Barely making it back to the relay station for the last shuttle, she forgets to lock up but leaves the master lock on. The next day, she joins the yacht club for further cleaning but stumbles and unknowingly loses her ID ring .As the yacht club discover that a worn-out engine room safety relay, Marika continues her cleaning work, unaware of having lost her ring. Before heading home, she hears from the crew that they are being released. The next day, as the yacht club continue to deal with the problem of the relay, Marika is called to the Bentenmaru by the crew who are locked out of the system. Marika then discovers that her ID ring is missing. The crew search the ship for the ring without success. Fortunately, Grunhilde discovered the ring and brings it to the Bentenmaru with the rest of the yacht club with the Silent Whisper. After bringing the Bentenmaru to the relay station, both the crew and yacht club sort through the assembled clutter. Staying behind, Marika discover a number of secret files with the ring, including the family recipe for pot-au-feu .
Another day, Marika comes into the club room to find the yacht club interesting in participating in the Nebula Cup dinghy racing tournament. However, aside from Ai, none of the yacht club have any real experience with dinghies, so Kane, having returned as advisor and acting somewhat strangely, puts them though intense simulator training in order to compensate. Afterwards, several of the group look up details on Hakuoh's past participation and learn that it had received a five-year ban after causing a major incident at the 13th Nebula Cup. On hearing that Hakuoh will be participating and fearing a repeat of six years ago, the Nebula Cup planning committee contact the Harold Lloyd Insurance Union to hire pirates (with a similar disregard for rules) for extra security. Not given the full details, Show gives the job to Marika and the Bentenmaru. Around the same time, Kane takes Ririka to a meeting where representatives involved in the non-aggression pact are discussing the Bisque Company, a group planning to target the Katos .
Assembling the yacht club on a beach outside New Okuhama City, Kane has them participate in a wind-surfing race to select their representatives for the Nebula Cup, despite some objections. During the race, the Bentenmaru fires a pulse into the atmosphere to stir up the winds and the waves. The first two places are taken by Natalia and Grunhilde, with Marika and Ai neck-and-neck for the last part of the race, though Ai ultimately takes the third place. On the day of the race, the yacht club leave for Calmwind followed by the Bentenmaru, with Kane seemingly back to normal .
On arriving at the Nebula Cup orbital station for the race, the yacht club are confused by the fearful and hostile reception from the staff and participants until they meet with Chiaki and learn of the incident that occurred at the 13th Nebula Cup (which Lynn is revealed to have played a part in). Marika goes to the chairwoman but is unable to get her full attention as she is busy. She does get permission to borrow a dinghy and goes to watch over the race from within, however after she leaves, the chairwoman learns that Marika is from Hakuoh Academy and goes after her in another dinghy, believing her to be up to no good .
As the race gets underway, the yacht club learn that the organisers have set the race up to replicate conditions from six years ago and the competitors have been training to get their revenge. Meanwhile, Marika is being harassed by the chairwoman. Suddenly a helicraft belonging to the Bisque Company appears and starts firing on the racers, not knowing which dinghy Marika is in. While Chiaki leads the others to safety, Marika flies towards the Bisque craft and identifies herself. Seeing her action, the chairwoman tries to help her but soon gets shot down. As Marika struggles, the Bentenmaru descends into the atmosphere to rescue her, but finds itself at a disadvantage. With some help from Ai and an atmospheric wind current, the Bentenmaru uses its frontal pulse device to shoot down the Bisque craft, though their last EM attack knocks out the electronics on Ai's dinghy. Ai continues the race regardless, using the stars to navigate, while the Bentenmaru returns to space. The race is won by Chiaki with Grunhilde coming second. A few days later, Ai comes in to talk to the others about the next race .
- Marika and the yacht club perform cleaning on their respective ships and Marika briefly loses her ID ring .
- The yacht club enter the 19th Nebula Cup, unaware of their school's actions and subsequent ban in the 13th Nebula Cup .
- The tournament organisers hire the Bentenmaru to provide extra security, unaware that Marika is from Hakuoh Academy .
- The Bisque Company make an attempt on Marika's life during the tournament .
|Episodes||19 • 20 • 21|
|Multiple||Recruitment Arc • Golden Ghost Ship Arc • Hakuoh Pirates Arc|
|Anime-Only||Nebula Cup Arc • Pirate Hunter Arc • Abyss of Hyperspace|
|Novel-Only||Three Ships Arc • Skull Star Arc • Bounty Arc • Wanted Arc • Timeslip Arc • War of Independence Arc|