"An impostor? Do you even know what're you trying to say!?"
- ―Dark Zagi
The alternate version of Dark Zagi (ダークザギ Dāku Zagi) was a dark giant called to the Earth by child scientists of a foreign country, Soso and Utsutsu. He was one of the few antagonists of Ultraman F and was the one who (accidentally) triggered the alternate reality Akiko Fuji's transformation into an Ultra-like being called Ultraman F.
Ultraman F Chapter 3: Dark God of Destruction
Dark Zagi was summoned by the child scientists Soso and Utsutsu from a dimensional tear made by their clone Bullton as he arrived on Osaka. Their main wish was to become beings whose existence transcends even humanity, Zagi instead ignored it, knowing that they only wanted to survive and instead transformed them into his dark giants, Dark Mephisto and Dark Faust respectively. He had no interest in their wish to create a new world but choose to watch their progress from afar.
When Dark Mepisto and Faust went on their killing spree, Akiko Fuji appeared and utilized the giant armor to become Giant Soldier F, facing against the dark giants. Fuji also called Zagi as a fake Ultraman, provoking the destroyer to join the battle as well. Zagi proves his efficiency by stopping the warrior's Mars 133 with his own hand and dispels every armaments of Giant Soldier F with Zagi Reflection. Ultimately, when all three dark giants fired their attacks on F, this caused Fuji to be mutated into Ultraman F. The Ultrawoman soon killed Faust with the Spacium Beam and defeated Mephisto with M87 Beam.
"A perfect death for dark giant Ultraman never exist, Zagi will revive anyway. Someday Zagi will gain the light, and the day where he will become a true Ultraman shall come."
- ―Fuji after reverting to her human form.
Zagi watched in astonishment that not only had he created a powerful opponent in Fuji but she has also become a genuine Ultraman despite inheriting Zagi's imitation features. Though F however stated that "Zagi is indeed an Ultraman, but was never referred to himself as such". Angered, Zagi was about to attack the city but was teleported by Fuji to another place. Soon, both engaged in a fight by teleporting to various cities in different countries and finally landed on the moon where both clashed against their finishers. Zagi was defeated after F's finisher penetrated his Energy Core, followed by a huge explosion. Despite his death, Fuji reassured that an Ultraman never dies, thus Zagi would gain his own light someday to become an Ultraman.
- Original Powers of Dark Zagi: It is safe to say that this alternate version of Zagi retained the same power as the original.
- Lightning Zagi (ライトニング・ザギ Raitoningu Zagi): Zagi's main finisher.
- Zagi Wave (ザギ・ウェーブ Zagi Uēbu): A dark version of the Noa Wave which heals only Space Beasts. He used it to heal Dark Faust and Dark Mephisto.
- Zagi Galaxy (ザギ・ギャラクシー Zagi Gyarakushī): Zagi's version of the Noa Galaxy, using a dark wave to summon meteorites from asteroid belt. He tries to attack Ultraman F but was thwarted by her counterattack.
- Zagi Reflection (ザギ・リフレクション Zagi Rifurekushon): Zagi can reflect any incoming projectiles, doing so to evade all of Giant Soldier F's cannons.
- Teleportation: Zagi is capable of instant teleportation to any places he desired.
- Dark Giant Creation: He was shown capable of turning humans into Dark Giants, transforming the scientist pair Soso and Utsutsu into Mephisto and Faust.
- Acceleration: Zagi is capable of striking his opponent with blinding speed that cannot be seen with naked eye.
- This Dark Zagi is mentioned to have a similar past to the original one, as shown being provoked when Akiko Fuji called him a fake Ultraman and refused to acknowledge him as a genuine one. The original Dark Zagi turned against his creators, the Visitors after realizing his true status as a rip-off of Ultraman Noa.
- According to the novel as well, Zagi had also fought against Zoffy and this caused Ultraman F to replicate the latter's M87 Beam.
- His battle against Ultraman F is a reference to the original incarnation's battle with Ultraman Ginga.
- Despite being a sinister villain, Fuji felt sympathy to Zagi for being a "fake Ultraman", even wishing him to become an actual Ultra someday. In fact for his minions Faust and Mephisto, their original incarnations met their deaths after finally redeeming themselves to the light.