You know what I just realized? No one ever told Neville of Sirius innocence. Yet he went to go on the rescue mission in fifth year when he thought he was in danger.
That means Neville literally just saw how worried Harry was, and just made a quick, and correct, decision that Sirius must be innocent. Neville dropped everything to try and help save someone he didn’t even know because his friends were worried about that person!
I’d declare that Neville is the kindest dude in that series if I didn’t already know that. And overall, Neville doesn’t get near as much appreciation as he should.