OOPArt (オーパーツ Ōpātsu) stands for "Out of Place Artifact". It was a device used by the Lost Tribes, each of which was wiped out by their specific OOPArt. Dark Phantom stated that when the weak use the OOPArt, they can't control it and lose themselves in the process, causing them to be consumed by it.
In Mega Man Star Force 2, at the IFL Tower Museum, an OOPArt was on display (which one varies depending on the game's version). Omega-Xis noted that the OOPArt was emanating strong EM waves. When Rogue attacks the museum, he attempts to steal the OOPArt with a Kamikakushi. Mega Man fights for the OOPArt, only to end up with Omega-Xis accidentally swallowing it.
Following this, the spirits of the Tribe started communicating with Geo Stelar and Omega-Xis. First they sounded insane, bugging Mega Man to give them his body. When Mega Man is confronted with several Murians at the same time, the spirits noticed his plight, and taught him how to use their power, allowing Mega Man to wield it and defeat the Murians.
In the Alternate Dimension, after defeating Apollo Flame for the first time, the spirit of the OOPArt returns, congratulating Mega Man for averting a future of destruction. It also reminds Mega Man on the fragility of bonds, which was what resulted in the Tribe's downfall.
In the anime, all three OOPArts make an appearance. However, the Sword of Zerker was the only one to be in a museum. The OOPArts were deactivated as the continent of Mu was sealed. However, the coming of Cepheus caused the seal of Mu to become undone, and the three OOPArts became active once more. When The Sword of Zerker was looked at with the Visualizer or the Star Carrier, a large amount of EM Waves were being released from it. The Sword of Zerker was targeted by Dark Phantom and Yeti Blizzard, for their own personal reasons, such as wealth or immortality. But in the struggle for it, Mega Man came and Omega-Xis accidentally ate it. Omega-Xis was scanned for a possible removal of the OOPArt, but it was too risky, as removing it could delete Omega-Xis. Soon, Geo was asked to locate the other two OOPArts by Dr. Vega.
The OOPArts were also being targeted by Rogue, and he attacked Mega Man for it. When Rogue and Mega Man battled a second time, Rogue defeated him, along with Lyra Note and Cancer Bubble. When Rogue attempted to cut into Omega-Xis' head for the OOPArt, the Sword of Zerker activated in self-defense and transformed Mega Man into Thunder Zerker, driving Rogue off.
Mega Man has also used the transformation in times of need, but it soon became out of control, as Mega Man transformed for a simple small virus deletion. When he transformed in his battle against Dark Phantom, the Sword of Zerker went out of control and began swinging wildly on its own and dragging Mega Man all around a desert resort. When Mega Man returned to normal, the truth came out. Just like in the games, Omega-Xis experienced great pains from the OOPArts power. When Rogue appeared again and battled Mega Man, Geo got knocked out when Rogue used Battle Cards in the fight. Then the Sword of Zerker pulled Geo into a dream revealed the real reason for its out of control: Geo hadn't proved himself worthy to wield it's power. So, the test the Sword had for Geo was to pull the Sword out of the ground. However, the Sword showed that Geo only had a little time, as Rogue began attacking Omega-Xis, who was carrying Mega Man unconscious body. Geo managed to pull the Sword out just in time to stop Rogue from delivering the final blow. Rogue showed great surprise at Mega Man's mastery over the OOPArt, before being forced to retreat. The sword then stopped going wild in Omega-Xis' body.
Soon, the next OOPArt was revealed, the Rock of Saurian. It was hidden in a cave inside a lake, that was the home of Plesio. However, the OOPArt caused Plesio to be seen by humans, even though he was made of EM Waves. this in turn caused a tourist attraction to take place, which greatly annoyed Plesio, so he took control of Gerry Romero and transformed into Plesio Surf to scare the people away. Rich Dotcom tried to take the OOPArt, but couldn't beat Plesio Surf, so instead thought to use Mega Man as a distraction. The plan worked and Rich took the Rock of Saurian.
The final OOPArt was the Star of Ninja. It was the treasure of a ninja academy, that was hidden deep within the grounds. Geo, Hyde, and Rich all competed to try and find the OOPArt, but had to avoid the traps laid. Mega Man managed to find it first, but was stopped Rogue, who attacked Mega Man. In a rush, Mega Man used Thundetr Zerker to try finishing the battle quickly. This made Yeti Blizzard use the power of the Rock of Saurian for a power boost. However, the activation of two OOPArts in the presence of the third OOPArt cause the Gate of Mu to open. Rogue tried to stop the Gate from fully opening by attacking it. However, this not only sucked Rogue in, but created a high gravity field on the cave, paralyzing everyone in it. But, Hyde, as Dark Phantom, was able to use his Phantom Claw as a way of grabbing the last OOPArt. When Mega Man reported this to Dr. Vega, she got upset and called Mega Man useless.
Now that all three OOPArts were taken, Dr. Vega was able to predict the battle for the OOPArts. The battle happened and when Mega Man and Yeti Blizzard fought, the two OOPArts reacted to each other and unleashed a horde of viruses into the city.
Eventually, Dr. vega decided to make her move and had Hollow battle and defeat Hyde and Rich and take their OOPArts. Having two of them made Dr. Vega reveal her true agenda: to open the Gate of Mu and awaken Le Mu from it slumber of 12,000 years to completely revolutionalize the world's EM Waves. She then ordered Hollow to attack Mega Man for the last OOPArt. Mega Man fought well and almost won, but Vega used the two OOPArts in her possession to heal and empower Hollow. This activated all three OOPArts again and the Gate of Mu was opened again. Hollow battled against Mega Man once more, but the battle was completely one-sided, as Hollow had two OOPArts and Mega Man only had one. Mega Man was defeated and Omega-Xis lured Hollow away from Geo. Hollow chased Omega-Xis and captured him, before extracting the OOPArt from him.
When Geo came to, he met with Lyra Note and soon found an unconscious Solo, who was healing from his wounds. Solo explained that he was the last survivor of Mu and that he was meant to guard the seal on Mu, which explains why he continuously attacked Geo for the Sword of Zerker. Solo explained that the three OOPArts each carried a third of Le Mu's power. Then Solo sturggled to transform into Rogue again to pursue the OOPArts from Vega.
Meanwhile, Vega ordered Hollow, and the newly recruited Rich and Hyde, to place their respective OOPArts into a stone monument to awaken Le Mu. Rogue arrived, but had to battle against Hollow. Geo arrived and managed to save Omega-Xis from being destroyed by a pool of purple liquid, meant to 'eat' EM Waves. Lyra Not and, late on arrival, Cancer Bubble lured Dark Phantom and Yeti Blizzard away. Bob Copper, who accidentally got taken into the Mu continent, told Mega Man to hurry and take to OOPArts before their powers were absorbed by Le Mu. Mega Man went to pull the Sword of Zerker out, but Vega quickly called Hollow, who had just defeated the injured Rogue, back. Bob Copper managed to delay Hollow from hurting Mega Man in time for Mega Man to pull out the OOPArt, transforming into Thunder Zerker once more.
However, this seemed to have caused a chain reaction, as the other two OOPArts also ended up being absorbed by Mega Man, allowing him to transform into the Tribe King. Hollow tried to fight Mega Man, but Mega Man became too powerful for any of Hollow's attacks to work. Mega Man Tribe King quickly destroyed Hollow with his Over Slash attack.
Mega Man, Lyra Note, Cancer Bubble, and Detective Copper managed to escape from the continent with the gate, but soon saw something terrible happen; Le Mu, now awakened, tries to force open the Gate of Mu to enter the Planet. Rogue appears and uses all his strength to push Le Mu back, while telling Mega Man to destroy the gate now that he has all three OOPArt's power. Mega Man questioned how, to which Rogue replied that "The three stones will guide you". Mega Man was then able to unleash the Czar Delta Breaker and seal both Le Mu and Rogue away.
The three OOPArts currently still exist within Omega-Xis.
- Before deciding on using the Noise Change system in Mega Man Star Force 3, Tribe On was considered to return in the game alongside two other Tribe forms that were dubbed "Pirate Mega Man" and "Angelus Mega Man". Their OOPArts are unknown, being assumed to be an anchor and crossbow.