Years after the defeat of the League of Villains and the death of all his friends, pro hero Deku, also known as Midoriya Izuku, comes across a shady-looking shop owned by a mysterious man who called himself the Phantom who proposes a deal to travel back in time and save everyone. Izuku doesn't make the deal because he actually reads the deals and finds the various loopholes. Amused, the Phantom proposes another deal without loopholes and Izuku agrees. As a gift for being the first one to actually discover all his loopholes, the Phantom gives him a book full of magical artifacts. These are magical artifacts so their effects and powers won't be affected by quirks like Eraserhead's.

Izuku goes back in time. However, his thinking changes because of the time he spends with the artifacts (each have a usually-sad-or-tragic-in-some-way backstory related to humans and desires). Instead of becoming a hero, he creates a vigilante group called The Witch Hunters with him as the leader. His vigilante name is Grimm. They not only fight villains but also corrupt heroes but unlike Stain, they let those heroes a chance to change and only kills them if they don't change for the better.

He also gave some people artifacts to help them. He gives a young Shigaraki (way before Shigaraki goes through the traumatizing event that led him into the hands of All For One) the Cinderella watch so he could fix the things he accidentally disintegrated. Shigaraki doesn't turn evil and is later adopted by Inko after he follows Cinderella's directions to find the one who gave her to him, Grimm. I'm thinking of maybe giving him the Musicians of Bremen MP3 player.

Young Shinsou gets the Wolf & 7 Sheeps chalk to help him fight since he has a non-physical quirk. The Wolf also becomes his friends since both of them are ostracized for being different. The Wolf also leads him to Grimm & Shinsou joins the team. I'm thinking of maybe also giving him the Godfather Death lamp and/or the Mary's Child fan. The lamp just goes with the aesthetic and the fan actually forces people to tell the truth immediately so it would help him with using his quirk.

Young Shouto gets the Golden Keys so he can have a save haven that no one could enter without his permission. He later joins The Witch Hunters and offers to use his haven as the base of operations. There's a meeting room and a room for each and every member (Shouto is still in control and can lock anyone in or out of the base and their rooms). Since Shouto already has one space-manipulation item, might as well give him another one: the Rapunzel gun which has the power to isolate people by literally sealing them away in a different dimension.

Izuku will not get One For All. Is your choice to have him use a subtle enough artifact (like the Trusty John tatoo) to get in the Hero Course or present himself as quirkless like he actually is go to General Studies with Shinsou (Shinsou won't use the magic chalk in the entrance exam because it would reveal that he is a part of The Witch Hunters).

The rest just loosely follows Canon.