But a katana is a sword there the same thing infact a katana is a retarded sword because its only Sharpe from one side
Single edged swords have the advantage of being sturdier than double edged ones, and with Katanas being already flimsy pieces of crap a second edge would just make them even worse. Not to mention that you'll rarely if ever use the backside of a curved sword to attack with, as it's harder to properly cut with it, allowing only for strikes, which require a sturdy blade to not break after a swing or two. Also learn how to spell.