You find a cigar box painted a deep red with intricate mahogany trimmings. Inside is several dozen miniature swords. They are about 5 inches long and far too small for anyone but maybe a fairy to hope to use them.

While attuned to this item as an action you can open the box and scatter the swords. When you do so the swords will levitate just before hitting the ground and then start to rise as they enlarge to full sized longswords, surrounding you in a sparse 10 foot sphere for the next hour.
After the hour is up they fall to the ground and shrink back to their original size. If you open the box they will slowly float into it, saving you the trouble of picking them all up.
Once you have used this feature you can not use it again until you complete a long or short rest.

While the swords are surrounding you, you have Half Cover against ranged attacks, you can make an opportunity attack against any creature that leaves this sphere without expending your Reaction, or as a Reaction you can make an opportunity attack against any creature entering this sphere.  Additionally, when you would make a melee attack you can choose to target any creature adjacent to, or inside, this sphere of swords with a magical longsword attack instead.