Sword, fencing and sword excercises in aikido training
Moving a sword, we learn to move ourselves like a samurai (japanese knight). This way we learn also to make the unarmed techniques better.
 
Katana is a japanese sword, the main weapon of a samurai.
 

The samurai were similar to the knights in Europe in the Middle Ages.
Like them, the samurai have fought for their Daimyo (prince) and also killed for him.
But:
what makes aikido so unusual is, that we use sword techniques but we don't kill or hurt anybody.

Aikido was developed from aggressive martial arts, but it does not contain any aggression.
 
The samurai treated their swords with a special respect. That's not unusual - their lives depended from their skills and from the swords.
We in aikido also respectfully treat our swords, although we don't practise with sharp katanas, but with bokken (wooden imitation of a samurai sword).