Dark Force is the main antagonist of Otomedius Excellent. She is a Bacterian superweapon created by the Gofer Sisters as part of their campaign against the G Organization, designed to crush Earth's defenses and obliterate the Organization itself. Though she is just a weapon, the Sisters treat her with great respect and equality, as they recognize she might turn on the Bacterians if she feels unhappy.
She first appears in the beginning of Stage 6, destroying the Gradian fleet, along with Dr. Venom. Realizing that the Angel Squadron was no match for Dark Force's great power, Operetta sent the Angels back in time to destroy Dark Force at her larval stage.
She pilots the Black Viper in your first battle against her in the Bacterian Mothership. Her Black Viper is armed with Laser, Ripple, Flying Torpedo, and Vulcan but has no Options. After you defeat her, she escapes, and transforms into the Death Bringer, the True Final Boss. She also appears as the boss of the hidden stage following the last stage. In this stage, all she does is send out Fans and fire three bullets every few seconds.
- After Dark Force in her Death Bringer form is defeated, she says, "I was spawned from human desire... So long as you exist... So shall I," which sounds similar to Bacterian's last words in Gradius III: "I was born... Out of the greediness of mankind. While men exist, so will I." This implies that Dark Force is a regenerated version of Bacterion and that their words were true.
- After you defeat Dark Force in her first phase and she escapes, you can see portraits of the final bosses of Gradius, Gradius II, III and Salamander 1 and 2.
- Either she's the current leader of the Bacterians, or the Gofer Sisters created her as a weapon of mass destruction. No matter which one it is, even when she's in her larval stage, she's very powerful.