The shape is not easy to see in this picture, but I'd say you could make a flat strip getting that tire-like shape ready and then use bend modifiers to achieve a similar deformation.
@Minjae_Jeong It would really help to know whether some or all of these faces are flat, or if there are any curves involved here. Is this on a cylinder? Do a little unzoomie for me.
Need some help here: :D How can i bend the flat one into the circle in Maya? Anyone know how to make a Plane from flat to cylinder? Or a plane bend? In Maya
Hey Perna! I have no idea how to model in the flat Shape which is coming after the box, without to destroy the round shape of the cylinder...and on the other side of the weapon the cylinder is normal round, not flat.
Just use ngons on the flat parts of the knife and then simplify the profile of the blades edge. Ngons on flat faces doesn't matter as it won't be seen anyway and it doesn't look like you'll do any sculpting on the knife.