There was surprising overhaul of sorts at Hogwarts School of Witchcraft & wizardry.
It seemed that the ghosts which were there before the famed Battle of Hogwarts had moved on and had been replaced by many of those who perished then.
Such as the Lupins, with Remus having additional wolfy ghost from his werewolf side and had taken the place of Gryffindor's House Ghost, Tonks assisting at sorting, which made even more impact on first years, and taking the Hufflepuff HG position.
Severus Snape who had taken upon Slytherin's House Ghost position, with a wound on the throat and a glower that scared nearly everyone off had taken to haunting Hedmisstress Office making sure she did not neglect any students again.
There had been a wonder of who would taken up a post of Ravenclaw HG post but the person supprised everyone. One Harrison Potter had died of aftereffects of his rough childhood, treatment at Hogwarts and the whole ordeal with defeating Voldemort after a month of struggling, weakening and writing a will.
During his death he managed to kick Sirius Black, suspended in The Veil of Death and reinstate him as Teddy's co-godfather.
And Harry was adamant in making certain to scare any and all bullies mainly in Ravenclaw, but also in all school. And taking cue from Snape he had very clearly and stubbornly haunted professor Flitwick with stories of Luna, Myrtle, himself.... And the small teacher in the end joins in making it his own mission.
Except the 4 Housegosts also poltergeist gotten kicked out. And in it's place popped none other than half of Terror Twins, Fred Weasley, which made George and the rest family frequent guests of school. As was Sirius with little Teddy.
Which evolved into Visit Your Ghosts Saturday.
Also without special accommodations, every other protector of Hogwarts had appeared to float here and there, chatting, circling, observing etc.
Harry had taken to visiting Sirius and Teddy on occasions, when he manages to breach the rule of ghostly hounting only the place of death.
In truly 'Harry Potter achieving impossible again™' manner he even managed to haunt the Dursleys to the extent, that had them loosing all scraps of normal reputation, a whole story being revealed and Dudley going voluntarily to reeducation center, to recreate himself outside of his parents influence.
Harry was very glad and approved all of this and changing of names from Dudley Dursley to Daniel Johnes, after said cousin gained himself a mentor and later became a helper and mentor himself.
And once a year on Halloween instead of bad luck happenings all ghosts and living had started a feast and collective reminiscing of "departed close ones".
Unknown to these living, all recent ghosts were sworn and agreed to stay only a hundred and Harry's "death age" years, then depart. Because as it happend every one of them didn't intend on sticking between plains of existence longer then absolutely needed.