(1) Cross the volcanic ash-filled Road 113 to Akiba Town.
(2) Continue down the road to Meteor Falls.
(3) Map of the inside of Meteor Falls:
Surf, climb the waterfall, and go inside the hole at the top.
Then go right down the stairs on the right.
Take a u-shape to the left and go up the stairs in the upper left corner.
After that, you'll run into a couple, so keep going up to the top staircase, go a little to the right (don't jump off the staircase) and you'll see Daigo, and then you can continue on with the main quest.