We are all bound to one another by Fate.
Within each of the greatest heroes lies immense power far beyond anything ever seen, and it can only be unlocked when they become linked with one another by Fate! Will you help them realize this power?
Accessing the Fate Link
In order to access the Fate Link, go to the hero profile of your 5-Star hero and tap the icon just beneath the PWR display. Alternatively, you can go to the Hero menu and tap the Fate Link button, which will display all heroes in your roster that have unlocked their Fate Link.
The Fate Link Screen
Either option will take you to the Fate Link screen, which displays your selected hero along with the portraits of three linking heroes. The two linking heroes at the bottom of the triangle will grant stat bonuses when activated, and the third linking hero at the top will grant a powerful passive bonus.
How to Activate 
In order to unlock the powers of the Fate Link, you must possess all of the three heroes displayed in this screen. In this case, Destroyer Roy needs to have a level 70 Last, level 70 Ruthtria, and level 80 Recast Witch.
If you possess the specified linking heroes, the Activate button will be available at the bottom of the screen for each of the three.
In order to Activate linking heroes, you will need to spend a new in-game currency called Destiny Coins which can be acquired at the store in the Tower of Fate using either Star Flake Stones or various resources in your inventory.
With the required Destiny Coins and hero levels, activating each linking hero will grant the stat bonuses specified next to his/her portrait. The third linking hero, which grants a passive ability, can only be activated once the other two linking heroes are activated.
With that said, the amount of destiny coins needed to activate varies for each fate, for example:
For Destroyer Roy and other heroes, 100 destiny coins is required for the first fate(The bottom left), 200 destiny coins is required for the second fate(The bottom right), and lastly, for the third fate, 300 destiny coins is required. (The top)
Yet however, some heroes have talents which can reduce the amount of destiny coins needed such as Airi
After activating a linking hero, you can spend more Destiny Coins to enhance the stat bonus they give up to 10 times.
Note: Activating linking heroes does not consume them or render them unusable in any way.
With all three linking heroes activated, your selected hero will be immensely powerful! However, there is a tradeoff to consider: with every linking hero that you activate, your selected hero’s COST will go up! If you find that your hero’s COST to be too much to fit in your squad, you can revert it to its original value by deactivating the linking heroes by tapping the Deactivate button next to the Activate button.
The amount of COST that a linking hero adds to your selected hero is displayed at its stat bonus tab.
Some heroes are special and do not require more COST after they have been fate, while others possess a talent that can reduce cost needed.
NOTE: some heroes that do not need COST after fate is mostly at the 3rd fate such as Ash
For a full list of all eligible heroes' Fate Links, go here .