Tears are also a weapon
This is by way of being an outline which might or might not get filled in anyone wants to adopt it, feel free, please credit me and send me a link
Harry Potter discovered at an early age that he could cry at will. He also discovered that if he cried silently when doing yard work, and cringed if anyone talked to him, it got neighbours threatening Vernon and Petunia. He discovered that crying at school got him out of breaktimes so Dudley could not beat him up, and even if Dudley called him 'crybaby' being the one in obvious distress gave him the moral high-ground. It even got him decent clothes, more food and new glasses made to prescription when a comment was passed that he looked like a cross between a political refugee and an escapee from Belsen. Petunia was not about to be accused of anything weird like keeping a concentration camp.
Crying at Hagrid bought him more time in Diagon Alley, and thus more books, and crying when Ron demanded to see his scar frightened off the crass redhead, and put Hermione into motherly mode. She firmly suggested that they should go into Ravenclaw where she could look after him, and Harry murmured about what a loyal friend she was. They ended up in Hufflepuff with Neville.
Harry's tears got him exempted from DADA, and as his prescription glasses emphasised how much he looked like Lily, his tears over not being allowed to study ahead had Snape scaring himself by feeding the boy tea and biscuits, and demanding later that he be removed from the Dursleys.
Harry saw no need to go on midnight prowls with the invisibility cloak which he viewed with deep suspicion. Strangers do not give gifts for no reason. He never found the mirror of Erised and he had no desire to court certain death on the third floor. When Neville and Hermione got excited about the Philosopher's Stone and took their information to Madam Sprout, who was inclined to try to get them to leave well alone, he cried at her until she promised to go and check it for herself with any teachers she could muster. Snape killed Quirrel, and ended his career as a spy as Voldemort's spirit was aware which side he was on.
He bought chocolate for Harry for arranging this.
In the second year, Harry cried at Dobby who had to retire to punish himself properly for upsetting the Great Harry Potter, so the dropped pudding never happened. Failing to get through the barrier, Harry cried at the first wizard he found, and was sent to school through the Floo. When Mrs. Norris was petrified, Harry cried all over Filch, who had no idea the boy was such a cat lover. He also cried more than Myrtle leading her to tell him all about the yellow eyes to get rid of him. Hermione was able to work it out from this, and Harry cried all over Snape who took a rooster down into the chamber after Harry opened it, and was the hero of the hour for killing the basilisk before any humans got petrified.
As soon as Harry heard about Sirius Black, he sent a tear-smudged letter to Amelia Bones asking for the trial transcripts to understand why his sworn godfather had betrayed him and his parents. Two months later a bemused Sirius Black answered a request to meet with no strings attached, and at Christmas Harry went home with his free godfather. He cried at Kreacher, who told him all about Regulus and Harry learned a new word. Sirius Black went on the rampage at Dumbledore with Kreacher and Snape as unlikely allies. The horcruces were all found and destroyed, except Nagini and Sirius found a ritual in the Black black library which allowed the removal of the one in Harry's scar.
When Amos Diggory started going on at Harry about Cedric managing to beat him to the snitch, Harry thought he had only one choice.
Harry burst into tears.
"Why is that bad old man attacking me verbally as if he thought I was Voldemort?" he sobbed loudly. "He's being rotten, anyone would think it was me who was two years older than his son and had been bullying him! I don't wanna go anywhere with him, he's nasty!"
"Dad!" Cedric was very uncomfortable. "You shouldn't act like that!"
Harry, however, had already launched his weapon of mass destruction.
Hurricane Molly.
Amos Diggory found himself verbally excoriated for gloating like a baby over a poor motherless child who did not have Cedric's advantages. Lily's and James' probable reactions were held up to Diggory, who paled at the idea of James calling him out, and at being called a coward because Harry was too young to call him out.
He left Cedric to go on to the game, and found he had something to do at home.
When Harry's name came out of the Goblet of Fire, he cried in front of the whole school, and refused to take part. Fleur decided that he was cute, and volunteered the information her father had found that a contestant had 24 hours to pull out. Harry was very grateful to Fleur. The false Moody called him a namby-pamby, and Harry agreed cheerfully.
When Fleur failed to rescue her sister, Harry cried at Fawkes until the phoenix rescued the little girl, and was consequently irritated with Dumbledore for his insensitivity over creatures of fire.
In the last test, Barty Crouch Junior kidnapped Harry, but Fleur also won and turned into her bird form at Wormtail, and killed him before he could start the ritual, and Harry cried at Junior long enough to be ignored so he could grab Wormtail's knife and stab him. He also stabbed Nagini before she bit Fleur, using the reflexes learned dodging Dudley and friends.
The homunculus form of Voldemort quietly died.
Harry married Fleur Delacourt and moved to France; Sirius had a villa in the south of France too anyway.