In the game, hollows are the most basic and most common of enemies. The more Final Tests you have, the stronger the potential hollows that you will fight. The hollows that you fight for basic levelling purposes are all basic and similar in name and attack-name, unlike the enemies in Shinobi Legends (where they are all based on actual characters and character's weapons).
For your Final Test, you must fight and slay the first hollows to have appeared in the anime/manga. These hollows get progressively stronger as you progress and you will fight the stronger and more deadly ones, similar to Ichigo as he grows into his Shinigami powers.