The Yokote is the point line which make the transition between the body of the blade and the kissaki or tip section. Yokote is not present in every blade style, such as the uncommon shobu zukuri style blade, whose tip is more suited to slicing than thrusting.
Beyond its aesthetic, the yokote, or tip transition line, serves a practical purpose. In fact, it's strengthening the tip for efficient thrusting. The katanas with a yokote are more piercing and could easily pierce the armor of the Samurai. The katana yokote lessens the impact's force and absorbs the shock so that it doesn't focus on the tip and harm the blade, while allowing for better perforation.