Vial of Sunshine: Professor at Hogwarts

This is an AU Harry Potter fanfic of a Hufflepuff student turned teacher starting in year 3 of canon.

The protagonist will not single-handedly gather all horcruxes and defeat Voldemort in wandless battle while beating all the death eaters present with a glance.
The progress against the Death Eaters will be logically sound (in my head anyway) advancement. Their defeat will come at the hands at someone who thinks about what he does and luck - though luck through actions the MC takes that make sense.
No reincarnation or prior knowledge of the story, no system or cheat. No harem, possibly a complicated love triangle at most. The MC will however work against the death eaters due to a personal grudge by working as a vigilante.

Ash Starkey or Ashbert Solaris Starkey (the magic of 7s is in the name length) is a pureblood wizard who should have died in the First Wizarding war but survived by visiting a maternal uncle for the birth of his cousin in February 1981. His paternal family gets wiped out at the same time due to the betrayal of an estranged uncle turned death eater, making him the last of his name.

Ash's great grandmother discovers his prodigious talent in potions early on and teaches him all she knows. Later taught by a hag and 2 potion masters, one of whom is his great grandmother, Ash uses his immense potioneering skill to achieve his Outstanding with distinction N.E.W.T.s and following potion master accreditation in the same year as his O.W.L.s in and after his fifth year in Hogwarts.

As prefect, he starts the famous Exchange Hall in his fourth year. A place where seniors are invited to share their knowledge and help out their juniors in spell works and potioneering.

In the summer before his sixth year, the Hufflepuff prefect meets Hermione and Harry of the golden trio while working in a potion ingredient shop in Diagon Alley and gets introduced to the lackluster efforts of showing muggle raised students the wonders, common sense and knowledge of the magical world. A lackluster effort he strives to turn into something better. Starting from a map for first time customers in Diagon Alley for first years to voluntary introductary study groups in Hogwarts where he explains common sense of the wizarding world to students in non-magical households.

This fanfic will not follow the plot of the books closely and rather than focus on Harry and his 2 friends, I will try to fill in the gaps of the original works and do a bit of world building. Among other things, I will introduce and expand on the concept of family magics, expand the world outside of Magical Britain and try and create other magical professions that aren't the 7 mentioned in the book: auror, professor, ministry employee, dragon wrangler, shopkeeper, Rita Skeeter and whoever else supposedly works at the Prophet and curse breaker at Gringotts.

DISCLAIMER:
Harry Potter and all its characters and universe belong to the author J.K.Rowling, who is not me.