A1, A9, A10, B3 for Nako?
She seems interesting.
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A1 - I don't think any nightmares Heck has bother him as much as the fact that dreams and nightmares aren't covered by his perfect memory. His nightmares are probably fairly normal - Being forgetful of things he should remember, performing naked, being in the dark in an unfamiliar place with something identifiable chasing him.
A5, A12 - Scars and injuries I'll answer together. I haven't really thought about it, but he must have had some injuries, his family being the way they are. Yet he's probably escaped some of the assassination attempts being one of the youngest siblings. His youngest sibling is a poisoner and probably has managed to poison him, but only when they were both children and it was more for practice. I'd say he has one scar from bird's talons on the back of his neck, but most of his injuries would have been healed.
A11 - What stresses him? Too much choice, too many possibilities. He likes to have a goal. He can deal with surprises if he has a target, but he doesn't like not having a plan at all. Also he gets stressed somewhat by completely unfamiliar situations, so anything to do with attraction, dating, having a crush - emotions are too messy and unpredictable for Heck to be entirely comfortable with them.