Spoiler alert for those who didn't watch the films or read the books.

#1: After passing the age of 21, people didn't tell him that he looked like his father, as James died at 21. Instead, people tell him he has his mother's eyes, which is green. However, some people told him he looked a lot like John Lennon. Harry wondered who the heck was Lennon, he wasn't a wizard and Harry never thought who he is, and why everyone was fussing over him.

#2: After the Battle of Hogwarts, Harry visits 12 Grimmauld Place, which was left in his godfather's will. Searching the house, Harry finds a stash of not wizard music, but Muggle music, music he listened to before Harry went to Hogwarts. Looking through the music, Harry finds some albums of Queen. Sure, he has heard of the band, but never knew about Freddie Mercury's death. Listening to We are The Champions, and Bohemian Rhapsody, Harry could relate a lot to the former, as it was a reminder of his victory over Voldemort. Harry then finds other music in the stash, finding copies of albums, he was interested in a particular album, Abbey Road. Like We are The Champions, Harry felt he was related to most of The Beatles' songs, as it reminded him of important parts in his journey and memories at Hogwarts. Harry now understand why that people told him he looked like John Lennon, they had eerily similar lives; both had absent parents and were raised by their aunts and uncles, and in their later years, became worldwide famous in their respective worlds.

Sources: https://www.instagram.com/p/DO2ioJ4k7t4/

Instagram

~SPOILER ALERT FOR THOSE WHO DIDN'T READ/WATCH THE BOOKS AND THE MOVIES!~

#1: George Weasley often looked into the Mirror of Erised whenever he came to visit Hogwarts. There, he imagined himself with his ears reformed and his twin, Fred coming right next to him. George tried to talk to him, but only communicated by waving and smiling. George never got over his twin's death and tries to find peace that Fred truly sacrificed himself for him and his family.

#2: Every year on the anniversary of Dobby's death, Harry comes to Shell Cottage and puts a pair of socks on Dobby's grave to remember him by as a free elf.

#3: On big events like Christmas, Dudley, his wife and kids, and Petunia would visit Harry and Ginny's family, with Ron and Hermione's and the rest of the Weasleys, as Dudley and Petunia reformed and accepted Harry and Lily. Vernon never changed.

#4: On the anniversary of the Battle of Hogwarts, Harry visits the Forbidden Forest and retraced his steps to remind himself the pain and trauma of all the lives lost, but to remind himself that he was the boy who lived.

#5: Draco always wears long sleeved clothing as he was a changed man and wanted to trace his dark mark so it could fade. He was ashamed of what it represented.

#6: Dudley left an empty seat at his wedding, hoping Harry would be there. Harry was busy at the time and sent a letter to him congulating him on his marriage.

#7: Neville planted a garden at the courtyard in Hogwarts to remember the fallen. Lavenders for Lavender Brown, Lilies for Lily Potter, Black Dogwood for Sirius Black, Daisies for Colin Creevey. Only Luna knew the meaning about it.

#8: Dean often drew sketches of the fallen so their memories would never be forgotten. Lavender and Collin were often worn from being touched too much.

#9: Molly often left a plate for Fred without realizing during family dinners after the battle as he was dead. Arthur took it away so nobody would notice.

#10: Harry never looked at the scar in his mirror. To his family, friends, and loved ones, it was a symbol of hope. But for him, it reminded him of all the lives Voldemort had taken. The scar was reduced to an ordinary scar when Voldemort was killed.

#11: Draco has a phobia of Thunderstorms now as it reminded him of crashing sounds from the battle.

#12: Ron stopped playing chess for a long time after the war, as it reminded him of the Queen smashing another piece reminded him of his loved ones, especially Fred.

#13: Percy wished he could never become Minister for Magic, or work at the Ministry at all. He regretted siding with Fudge when Voldemort returned, fearing he would get fired but made his family upset, which Percy never wished happened. Percy was equally traumatized by Fred's death as he was the first to witness it, along with Ron, Harry, and Hermione.

#14: Harry suffered from intense PTSD after the battle ended. He had a nightmare once in a while, so he took potions to have a peaceful sleep.

#15: Nobody told Harry he looked like his father when he turned 22 since James died at 21. People still tell him he has his mother's eyes.

#16: Colin's camera was found among the wreckage after the Battle ended. Dean restored it and discovered the last photo taken was Colin and Dennis smiling right before the Battle.

#17: Harry used the invisibility cloak after the battle ended to see the Dursleys moving back to the house. He wanted to see if they reformed. Only Dudley and Petunia did, Vernon wasn't with them.

#18: Harry found a pile of fresh flowers on Dobby's grave. He never asked anyone, even Bill or Fleur, but he liked to think it was his house elf Kreacher.

#19: During Colin's funeral, Harry remained silent for the entire funeral. At the end, as everyone left, Harry left a photo of him taken by Colin with his autograph on Colin's grave. It was the only autograph Harry gave (minus the autograph he gave to the man at King's Cross if you believe the Cursed Child is canon).

#20: Draco attended Fred's funeral without anybody noticing. At the end he visited Fred's grave and he broke down.

#21: Harry always wore his round Windsor glasses even though the Elder Wand repaired his eyesight. He felt guilty that the wand killed so many of his friends.

#22: McGonagall sent Pansy Parkinson and the Slytherins to the dungeons before the battle so she didn't want their Death Eater parents to be killed.

#23: Draco wasn't a villain, he was a misunderstood villain. He wanted to be friends with Harry, but as he didn't want to fail his parents, he became mean.

#24: Sirius always believed James was resurrected by Harry.

#25: Petunia fainted when Harry and Ginny went to the Dursleys right before their marriage in their wedding clothes, as Petunia thought it was James and Lily resurrected.

#26: At Luna's wedding with Rolf, Luna left front row seats for the people and friends that fallen.'

#27: Ron asked his parents if they could adopt Harry.

#28: While searching Lupin and Tonks' house after the Battle, Harry found adoption papers with his name in it.

#29: Snape hated teaching Ginny because he looked so much like Lily.

#30: Even though Teddy was raised by Ted Tonks, Harry and Ginny viewed Teddy as his adoptive parents.

#31: George couldn't produce a Patronus because his happiest memories were from being with Fred.

#32: James had to hold back tears when Harry turned up to Sirius and Lupin for advice.

#33: Voldemort and Bellatrix never had a daughter, as Voldemort never wanted an heir and Bellatrix had a god relationship with Voldemort.

#34: Vernon tried not to let Petunia and Dudley head to Harry and Ginny's wedding, but they refused.

#35: Harry danced with Molly at the wedding after party so Harry could be reminded of Lily.

#36: McGonagall was the officiant of Harry and Ginny's wedding.

#37: Harry left a couple of seats for James, Lily, Snape, Sirius, Lupin, Tonks, Fred, Colin, Dobby, and Moody at his wedding to remember them.

#38: George named his son Fred after his brother. Fred looked a lot like his late uncle.

#39: James Sirius and Lily Luna has a striking resemblance to James and Lily.

#40: Harry slept right next to his kids and Ginny just in case if something happened.

#41: Albus Serverus looked like a mixture of Dumbledore's and Snape's.

Most of the headcanons I got from:

https://www.instagram.com/p/DG-THhaoDdt/?hl=en&img_index=1

Instagram

https://www.instagram.com/p/DHQZGc5IUIx/?hl=en&img_index=1

Instagram