Item Drop Cats are Cat Units that can be unlocked when completing certain stages. Some only have a chance of being unlocked, while others are guaranteed. For units that only have a chance of being unlocked, using a Treasure Radar will increase the chance to 100%.
There are some unlockable Cats in the Stories of Legend, the first one will appear in sub-chapter 18. Cat units dropped in the Stories of Legend are necessary to use in some of the more difficult stages, such as Awakening, Crazed and Manic Stages.
Each Monthly Event has an exclusive cat unit. Clear the Event Stages to unlock them. The first stage of the event has an extremely low chance to unlock the unit, but each stage has a slightly higher chance than the last. Their True Forms can be unlocked by playing the Awakening Stage available during the Monthly Event period.