3Dropped by
the opening hit
It hits enormously hard against anything at or near full health and ordinarily against everything else. That makes it a first-strike weapon. You open on a fresh target, take the huge chunk, then either finish off something small or switch to a weapon that does not care about health thresholds.
reach and knockback
The blade is physically larger than nearly anything else available at this point, and the swing covers a wide arc with heavy knockback. Early Hardmode throws crowds at you constantly, and this is the tool that opens space when you are surrounded. Critical hits multiply the knockback further, so crit modifiers make it better at shoving than a straight damage roll would.
The same reach makes it a fast harvester in compact Glowing Mushroom farms, where you want a whole column cleared without repositioning.
where the design comes from
It is the Buster Sword from Final Fantasy VII, down to the red grip and the pair of red and green dots near the hilt standing in for materia slots. The Keybrand is its deliberate mirror: that one hits harder as a target weakens, and it points at another Square Enix sword.