The Lv.★ Giant Blade is the 8-Bit Boomerang?, which is based the Boomerang from The Legend of Zelda. It was added to Hyrule Warriors with the Master Quest Pack DLC. In Hyrule Warriors: Definitive Edition, instead of appearing as a separate Weapon, the 8-Bit Boomerang? replaces Biggoron's Sunblade when the "8-Bit Weapons" Setting is turned on in Game Settings within the Settings menu.
The camera zooms in behind Impa as she closes in on her targets. The screen turns dark until it is almost black - aside from Impa who then slashes with her blade, 'cutting' the screen back open and damaging foes. This attack hits in a wedge shape ahead of Impa.
Other Warriors make use of the Giant Blade in certain Adventure Mode battles: