This guide explains how to solve the hidden button puzzle in Fischl’s Northern Summit to obtain the Red Energy Crystal and the Heaven's Rod. The Heaven's Rod, while costing 1,750,000 C$, boasts impressive stats. Locating the Red Crystal requires finding and activating five buttons scattered across different islands, after first collecting the three other Energy Crystals.
Finding the Five Buttons to Unlock the Red Crystal
The five button locations are detailed below:

1. Moosewood Island: The easiest button to find. It's located behind the leaderboard, near the pier, close to the ground.
2. Roslit Bay: Proceed inland from the pier. Near the campsite, you'll find the Angler NPC. The button is hidden amongst logs on the ground near him.
3. Forsaken Shores: Head to the right side of the island, towards the watchtowers. A red glow is visible from afar. The button is within the watchtower closest to the pier.
4. Snowcap Island: This button is well-concealed. Go to Upper Snowcap and locate the Wilson NPC. The button is hidden within the wooden fence next to him.
5. Ancient Isle: Visit the unfinished lighthouse. The final button is situated on the side of the entrance.
After pressing all five buttons, return to the Glacial Grotto and speak with the NPC near the large crystals. This will unlock the passage to the Red Energy Crystal.
Video Walkthrough (Note: A video walkthrough would be included here if one were provided in the original text. Since it's absent, this section remains descriptive.)
A video walkthrough would visually demonstrate the exact location of each button, providing a clear and concise guide for players. It would show the player navigating each island and interacting with the button in each location.
Remember to collect the other three Energy Crystals before attempting this puzzle. Good luck!