What to do in the Flowerful Tower mystery room in Disgaea 5?

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Playing Disgaea 5, I found a mystery room in the item world which looks like Flowerful. There is a pirate at the entrance saying "What's at the top of that tower?". I have explored the map, and certainly there are several pillars, but I cannot seem to find any way to get any higher up.
I couldn't find anything in this map. What am I supposed to do here, and what is there to find?
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Disgaea 5 - Prinny Mystery Room Mayhem!
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