The part where he's looking out over the cliff is the last bit of his story you can access now. He'll be a returning character who will show up in future updates though, so I'm glad you are interested in more of his story. You can gather crystals from three of the large crystal deposits in the cave. There is one orange one that doesn't supply any, this was a mistake on my part, so I'll fix that in the next patch, but you can still collect all the requisite crystals (you are correct, they are used at the summit). There is a large deposit of blue crystals at the top of the cave, far right, an orange deposit in the right middle across a bridge, and a purple deposit down a rope at the bottom left. Hope this helps.