The Tree Key

As you explore the labryinth, you are sure to have come across several locked doors. The only way to unlock these doors and explore what is beyond them is to receive the Tree Key. However, it's a very elusive item and many are bound to miss it.

So, here's the location: The Key is located on Floor 17 at C1-E2. To reach this spot you must fall from Floor 18 at either points E1-B5 or D2-C5. Selecting "Check," a guard will talk to you and sell you an unidentified item for 10,000en.