Choosing a Heroic Ability happens in Step 4: Invest XP. Does this mean you have to "purchase" this ability?

Heroic Ability changes the playing field dramatically, and so puts heroes on a different level (I like this!).

I know that you have to split your XP between Characteristics, Skills, and Talents as you see fit, but since they mentioned it happening during this step, I was a little confused as to whether it cost XP or not. It doesn't mention it anywhere, so I assume not, just wanted to get some clarification.

No, they don't cost XP. They are just another aspect of your character. I think it's put there so you had a better idea of who you character is and what Heroic Ability would work best.

I think that is a credible speculation. Thank you!

On page 79, second paragraph in Realms of Terrinoth ... "Your character receives ability points based on the XP they gain through play. Every time your character’s XP total increases by 50, they gain one ability point to spend." And that page they start listing the upgrades you can purchase and how many ability points they cost. A very cool system! Reminds me of the Signature Abilities from the Star Wars RPG.