When it comes to the ultimate offensive devices, sheer power is always required. The strongest anime arms and devices pack enough power to not only defeat enemies with ease, but potentially doom everything around them - including those wielding them.
Some devices, like the Bustermarm of Fairy Tail, are impossibly big and can cut through anything. Others, like the Punisher from Trigun, pack incredible power. Then there are the likes of Ea from the Fate series, which literally created - and can end - Earth itself. If you ever find yourself facing a device like these, you'd better hope your opponent doesn't know how to use it.
Though technically a sword, Ea boasts more powers than merely the ability to slice and dice. Ea cannot be replicated, as it's made of materials that are not of this world. Powerful enough to end the entire planet, Ea created the world by cleaving it away from the heavens.
Not only does it have these incredible primordial abilities, it holds knowledge of fundamental truths about the universe. Only one person, Gilgamesh, can truly wield this incredible sword.
The Silence Glaive is the only spear used by Sailor Saturn. Its abilities include conjuring force fields, creating blasts, and dooming entire planets. The glaive also causes worldwide earthquakes, massive gusts of wind, and ultimate demise.
When Pharaoh 90 tries to absorb Earth, Sailor Saturn silently swings the glaive down to the ground, obliterating Pharaoh and Earth.
Few devices match the formidable powers of the Murasame. The blade carries a toxic curse that stops a person's heart seconds after entering the body. With no antidote for it, the only way to survive an offensive strike requires amputating the afflicted body part before the curse reaches the heart.
Murasame also possesses a trump card called Little War Horn, which activates when the user cuts themselves with the Murasame and successfully resists the toxin. This offers a short burst of power, but in exchange, the user experiences permanent chronic pain that remains even after the Murasame breaks.
Only Grim Reapers wield such scythes, and they are every bit as powerful as that designation implies. The scythe can be used to view a human's Cinematic Record, which allows Reapers to decide whether or not a person deserves to live. If they decide to slay them, Reapers use the device to sever the connection between the person's soul and their body.
More than merely tools of doom, the Scythes can also be used during a melee. They're powerful enough to cut through anything, including another Grim Reaper. The only thing impervious to their powers is another scythe.