You can find a variety of Hores characters that can be convinced to join your Rank.
How to Unlock EVERY Hero in Xenoblade Chronicles 3! (Class guide)
In Xenoblade Chronicles 3, preparing for battle requires the use of heroes. So inviting a hero to your team is a good idea even if you don't need it, especially if you're playing on more complex difficulties or facing super bosses.
Heroes are essential for chain attacks and masking any weaknesses in your party line-up, in addition to the added benefits of having a seventh party member.
After chapter two, the hero system is readily available. It unlocks automatically, so you can't miss it, but due to some plot twists, you really can't invite your first hero until you've traveled through more of the Ribbi Flats or around a third of the way through the chapter.
