Bonds

Bonds represent the ties and trust between the commander and their followers. By interacting with heroes and giving them gifts, you can increase your Intimacy with them. By increasing their Intimacy levels, heroes will bring out their inner strength and the player can unlock exclusive voice clips as well as battle scenarios in each hero's Gate of Fate. You can give heroes gifts by selecting a hero inside of the Bonds menu from the main screen then selecting the Gifting option.

Intimacy
Intimacy represents the relationship between you and your allies. When a hero's Intimacy reaches certain levels, their Bond Powers will be unlocked. By upgrading their Bond Level, their attributes will increase.

Every hero has a different personality and different gift preferences. For example, the Dark Princess Lana's favorite gift is a Black Cat while Bernhardt's is a Globe. When you give your heroes their favorite gifts, your Intimacy with them will increase even more! A hero's preferred gifts are automatically moved to the far left of all owned gifts and have the words "Intimacy Up" displayed on the picture. Non Gem gifts of SSR rarity are considered unique and will grant a bonus of triple Intimacy Points to a specific Hero.

Gate of Fate
SSR and SR units will have explorable memories known as the Gate of Fate.

Enter a hero’s Memory Gate and you can experience critical moments in their stories, the battles that shaped them, and the unforgettable dialog for which they will forever be remembered.

A hero’s Memory Gate scenarios are unlocked once you reach a certain level of Intimacy with them. These stages allow you to accompany them in their past battles and you will also have a chance to obtain Memory Shards for these heroes!

After their Gate of Fate scenario has been cleared, the can be swept daily to gain additional Memory Shards. For SR characters, they can sometimes gain 2 memory shards per sweep.

Not all Heroes have a Gate of Fate. Most will gain their unique scenarios in a later update, but R characters (aside from Lester) are unlikely to get Gates of Fate scenarios of their own.

Bond Power
Bond Powers grant your heroes and their soldiers passive enhancements. When a hero's Intimacy reaches a certain level and certain conditions are met, their Bond Powers will be successively unlocked. When unlocking new Bond Powers, there is a one-time Trinity Crystal reward.

Each Bond Power will grant passive boosts to a hero's or their equipped soldier's stats. To upgrade them, heroes will require Heart Keys and eventually unique Bond Keepsakes (not Gifts) for further upgrades. These materials can be found in the Bonding Realm, Eternal Temple, and later Time Rift stages.

Each task required to unlocked each character's Bond Power are listed below:

Eternal Temple
Eternal Temple is a battle in the Secret Realm that grants Bond Items to further increase your heroes' potential. Specifically, they can upgrade the center "Heart Bond" in the Bonds screen. Not all heroes have their center section unlocked yet and will gain theirs in a later update. Heart Bonds grant passive defensive stats, Health Points, Defense and Magic defense as well as unique effects base on the Heroe's current Class.

A list of materials required to upgrade Heart Bonds can be found here, Center Heart Material Requirements