Here's a brief and crude description. Samurai usually wore two swords in a pair of long (katana) and short (wakizashi were shorter katana and tanto were more like daggers). The katana is a 2 handed weapon, you often cannot attain enough speed or strength against an armored opponent using a sword in 1 hand, especially for draw cuts. We know historically, the wakizashi was used for:
-Close quarters, where an opponent was too close to use a 5 foot long blade.
-A shorter blade was lighter and had a shorter handle and could be manipulated easily with a single hand and be used extremely close to slide between the armor plates of a downed opponent or through the front of an armored helmet.
-If the katana was damaged, broken, or disarmed, the wakizashi was a side-arm.
