For me it's a tie between the Shimada bros and Cassidy. Like Cassidy was basically living the life of Sons of Anarchy and was the BOSS, and who is responsible for his arm???
And Hanzo and Genji are just so sad, they both have issues with their mom and dad but only Genji has managed to get help, meanwhile Hanzo is going alone discovering his personality and interests, having to rely on Kiriko and her parents for the familial comfort he lacks...
These three got me into Overwatch way back in middle school and I'm still obsessed to this day about their stories! Every update I look at their skins, their new voicelines and interactions with other characters, BLIZZARD PLEASE JUST GIVE US STORY MODE! I NEED TO KNOW THE DETAILS!!!!