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The fusion of Sakura, Sugar, and Noire was of immense proportions, and it contained large added parts made exclusively for their fusion by William through all this time, including a giant and upgraded gamma blade, powerful force barriers, and all sorts of long-ranged gun machinery!
Additionally, they were able to launch powerful rocket punches that exploded on contact, and followed their foe until they hit! This also included their giant tracking missiles, but the rocket punch was cooler!
Also, they were able to recreate a new fist of metal with some mana, so they were able to easily rocket punch entire battalions of giant ocean dragons by themselves!
And well, they used the other weapons too.
Including a giant chest cannon!
"Activating chest cannon!" said the three girls at the same time, as their chest opened into an enormous cannon, charging mana, and firing a devastating ray that pulverized anything in front of them!
Check "The Protagnist's Sister Is Actually the Strongest"!