From an orphan, to being taken in by his secret agent of a father who decided it was a good idea to take a child on hits with him to... science experiment and trained weapon. Heero's life is a wreck tbh. Pity him Mama Sarah, but not too much because overt pity'll make him clam up like no other. He makes a good sad puppy squish anime boy, despite what he thinks on the matter.

I figure like every classic introvert, Heero has an easier time communicating via text than he does in person. Gives him an out to be more.. emotive. And then people who only know him via the network can be surprised at how he's a very -_- guy IRL.