Duminas' creator told her that she was a mistake that shouldn't have ever been created. She questioned why to many questions such as her existence, the reasons for her creations, and the reason why she's a mistake. The creator replied once more with the same answers, which led to Duminas killing her creator by accident.
She wandered through space for years, interacting with various alien civilizations. She ended up creating three homunculi, and thought of them as her own children. Once Duminas arrived on Earth, she found out about the existence of the Time Flow Engine, and decided to use it in order to go back into the past, and question her creator's intentions once more. She sent out her three homunculi, and had them assist various organizations in order to capture the Excellence.
Duminas managed to capture Raji and Mizuho, and requested their assistance in creating a new Excellence unit with a working Time Flow Engine. Raji agreed, as did Mizuho, and they went to work. Raji and Mizuho secretly planned to rig the Time Flow Engine in order to damage Duminas and escape.
After Duminas' Time Flow Engine was completed, she used it in an attempt to finally find out the answers that she had been wondering about for years. As soon as she started it up, it malfunctioned, causing massive damage to Duminas, forcing her to retreat.
Raji explains that a single Time Flow Engine by itself wasn't enough to allow them to time warp. The three homunculi tried to figure out ways to help Duminas' condition, and all three decided that they were willing to sacrifice themselves for her. Duminas objects, but later accepts their decision. Since it would take time for Duminas to rebuild them perfectly, she offered to make some changes for them. Dispinis wants to be kinder, Lalia wants to be manlier, and Tis wants to have a more adult body.
The three homunculi sacrificed their life force in order to revive Duminas at full strength, leaving behind their bodies which were still determined to protect Duminas, even in this state.
Once Duminas was defeated, it transformed into a second form. She transforms once more after its defeat, causing her to be in her third and final form. Once Duminas is defeated for a final time, she cries about not knowing the true reason for her failed existence. Mizuho told her that she realizes what the answer to Duminas' question is, and it's that Duminas is a human-like creation herself. She hated others that wouldn't accept her, she had a constant desire for knowledge, and she always tried to protect herself from the harm of others, which are all qualities that humans have. Duminas did not know what the creator intended to create, or why she was considered a failure, but she did manage to find out some truth regarding her existence shortly before her death.