A Great Legendary Hero Gathering! The Digimon All-star Showdown!!

'''Legendary Digimon Heroes are assembling to battle Quartzmon. But one more hero is needed, and Tagiru must fight the other Hunters for the spot.'''

Synopsis
After the tower that holds all of the digitalized humans turns into, Ewan Amano realizes that the Hunters are protected by their Xros Loaders. Quartzmon gets ready for a second attack, creating a Myotismon, which prompts the others to flee. The hunters gather at a small island that is protected by, where the hunters and the Old Clock Shop Man are waiting. The Old Clock Shop Man asks Mikey Kudō if he remembers the island, which he replies that it was the place that he fought Lord Bagra a year ago. The Old Clock Shop Man explains that that fight had brought Quartzmon into existence, as well as leaving behind the last of Lord Bagra's powers behind, which would become a weapon to hunt Quartzmon with. The Old Clock Shop Man explains that Quartzmon is a distortion of the human world's expanding digital power that came alive during the fight with Bagramon. Quartzmon had changed into particles that expanded DigiQuartz across the globe, which became a limit to the number of Digimon that could be out at one time. Quartzmon then brought Digimon from the Digital World to steal their data and gain more power, most of which had gathered in Japan because Bagramon's fight had occurred there. This was countered by a plan of the Old Clock Shop Man, who had enlisted several children to Hunt the Digimon before Quartzmon could steal their data as well as dealing with any other lost Digimon that would have ended up overseas. However, more people were required to deal with this problem, so the Old Clock Shop Man had brought others from the dimensions of Digimon Adventure/Digimon Adventure 02, Digimon Tamers, Digimon Frontier, and Digimon Data Squad to help. This included Taichi "Tai" Kamiya and Marcus Damon, who were the heroes of their respective dimensions. The Old Clock Shop Man explained why he didn't want Mikey to join the Hunt; that it would throw off the balance because Mikey was the hero of this dimension, and that the Hunt was also a way of training people to use the weapon made from Bagramon's power along with the help of the six heroes, the one to use the weapon being the best hero. Quartzmon draws closer, so Mikey, Christopher Aonuma, Nene Amano, Ewan, Angie Hinomoto, and Jeremy Tsurugi are asked to deal with Quartzmon and the copied Myotismon, Angie and Jeremy getting an orange and teal Fusion Loader respectively, symbolizing the courage and friendship they used to help digivolve into. Angie is given and  while Jeremy is given, and the six members of Xros Heart head off. Before they fight, Shoutmon notices that was inside Nene's Xros Loader, but Mikey says it doesn't matter since they are all a part of Xros Heart. Ewan uses DigiXros on and, Nene DigiXrosses Mervamon and Beelzemon, Jeremy DigiXrosses Ballistamon and , Angie DigiXroses Dorulumon and , while Mikey and Christopher digivolve Shoutmon and , then Double Xros the two. Meanwhile, Clockmon has sent the remaining Hunters into an image space where they can decide who is the best and use the Brave Snatcher. Tagiru Akashi and volunteer as well as Ren Tobari and a few others, but Ryouma Mogami proclaims that he cannot hand the honor to anyone else. Therefore, and  are to fight to determine who is the best Hunter. At the town, Xros Heart has managed to defeat most of the Myotismon, but Quartzmon creates MaloMyotismon (Fusion) and VenomMyotismon (Fusion), which defeat their Digimon. Mikey tells Shoutmon to stand up, who in turn responds that he has to fight for the sake of his juniors. A voice from above approves what he says, revealed to be Marcus and Agumon Burst Mode, the former punching a VenomMyotismon into two others. The two of them introduce themselves, while Agumon (Adventure) complains that Marcus's Agumon can fly. Tai tells him not to mind this, and they introduce themselves as well. A VenomMyotismon tries to attack them, but Magnamon (Adventure) blocks the attack with his own. Davis Motomiya introduces himself, saying that Tai is his senior but they are the same age at the moment. The confusion is cleared as Takuya Kanbara elaborates that they are from different times, and introduces himself while noting that though he doesn't have a Digimon with him, he is fine. Takato Matsuki claims how cool it is to see Davis and Tai in action, and introduces himself as a Tamer with Guilmon. Tai says he can't be shown up, and warp-digivolves Agumon while Marcus warp-digivolves his Agumon as well. Takato biomerges with Guilmon while Takuya fusion evolves into Aldamon (Frontier), who flies up into the sky along with WarGreymon (Adventure), Gallantmon (Tamers), and ShineGreymon (Data Squad), as well as Marcus. Meanwhile near and ancient pyramid, Joe Kido defeats a mini-Quartzmon, then notices that the others are gone. Gomamon (Adventure) tells him that they all left to go to Tokyo except him, leaving Joe shocked. Magnamon degenerates into Veemon (Adventure), Davis complaining about how Magnamon can only be used for a short time. But Ken Ichijouji and Stingmon (Adventure) show up along with Matt Ishida, MetalGarurumon (Adventure), and Takuya's friends. Kumamon tells Aldamon that he brought all of the Spirits, leading him to digivolve into Susanoomon (Frontier) while Veemon and Stingmon DNA digivolve into Imperialdramon Fighter Mode (Adventure) and Wargreymon fuses with MetalGarurumon to make Omnimon (Adventure). Jeremy confuses these with DigiXros, but Tentomon explains each of the Digivolutions. Additionally, Grani returns to Gallantmon to make Gallantmon Crimson Mode (Tamers) and Marcus changes ShineGreymon into ShineGreymon Burst Mode (Data Squad). Along with Marcus and OmniShoutmon, they manage to defeat all of the copied Digimon but did not harm Quartzmon at all. In the image space, Astamon has managed to defeat Arresterdramon, making Ryouma the candidate. They return to the island along with the legendary heroes, who help Ryouma drag the Brave Snatcher out of the sea. But Ryouma claims that it is troublesome for all of the heroes to be there, so he attacks Mikey and OmniShoutmon with the Brave Snatcher, injuring them gravely. Ryouma announces that he was an ally of Quartzmon from the start, shocking the rest of them, Quartzmon confirming this. With Mikey injured, the Brave Snatcher is again sealed in the ocean, unable to be used as Quartzmon looms closer.

Digivolutions
(Number indicates order of occurrence.)