Albus Potter and the Vampire's Oath by SortingCloche

The tale of Harry Potter ended with the defeat of Lord Voldemort and the start of a new age of peace in the Ministry of Magic and the wizarding world.

 The tale of his second son, Albus Potter, however, starts with this, and with his journey to Hogwarts School of Witchcraft and Wizardry. But in his first two years at the school for magic, Albus finds that his story will not unfurl as smoothly as one might expect in such a peaceful era. He finds himself confronted with a Hogwarts in turmoil, with a new Headmaster that seeks to chip away at the school's foundation as well as a student body that shuns their own kind. He finds himself opposing his family - such as his very talented, popular older brother James and his best friend and cousin Rose Weasley - and defending those who should be his enemies - such as Scorpius Malfoy, son of the ex-Death Eater Draco Malfoy, Emily Black, a self-centered and bratty girl with a big secret, and Katsurou Sen, the mysterious youngest son of a wealthy wizard family who is almost never seen. Albus even finds that his identity and desire to honor his father, once seeming so simple and sincere, could lead him onto a path he never imagined. Hogwarts has become a twisted Wonderland, where everything that had seemed good outside of the school shows itself to wicked, and everything that had seemed wicked...could possibly be good.

In the midst of all this, danger lurks in Albus Potter's future -- a danger that he will have no choice but to face differently than his famous father would have.