A large caliber handgun with a long, gigantic barrel.
It can hurt an undead due to its large bullets and high kinetic energy. However, it also has a strong recoil, which may injure the wielder's arm.
The gun itself seems based on the Wildey Hunter .475 Wildey Magnum, manufactured by the company known as USA Firearms Corp.-Wildey Guns of Winsted, Connecticut. An important fact is that the gun in the anime uses rounds called D- Point from which the gun derives its name. Similarly, the Wildey Hunter derives its name from the .457 Wildey Magnum round which was designed for this gun. Real life does not trump imagination this time, since the real round (although rather powerful since it is intended for big game), does not have nearly enough kinetic force to match the mythical D-point round.