Starting from Section two of Chapter Three, talk to Mr. Oshiro and enter the next zone. Make your way around the books to find Oshiro in the center and talk to him again. He'll open up a few paths, one of which houses the crystal heart.
Heading back right, go down at the first intersection of paths, then up at the second intersection of paths to come to the correct zone. Jump and dash over the orb wall and enter the next zone where Leo will be trying to get into the vents. Look up at the top-left corner to see a small opening that you can climb into. It is currently blocked off, but we'll return soon after unblocking it.
You'll pass through 4 zones to reach the button that makes the books go back home, and as you pass through zone 3, take note of the books blocking the lower left corner of the room. We'll come back through there very soon.
After activating the button, look at the right waterfall to see a small opening in the ceiling. Dash into it to reveal a path back to the previous rooms. You'll start back at the third zone from where Leo was, and you need to make your way back to the room where we found Leo trying to get into the vents.
From there, dash into the secret area we found earlier that was blocked to find it now open. Go through the ceiling to find the Crystal Heart floating there, waiting patiently for you. Dash into it and enjoy your achievement.
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