The Pen and the Sword by Jonathon Wolfer

Nick gets a pen and the ability to document the supernatural world, Mina gets a sword and super powers. Nick does not think this is remotely fair.

In 1986, High School Freshman Nick Stanton moves from New York City to a small fishing community in Connecticut called Kelsey Town. He has always been quiet and a loner, seeing things in the shadows he’d rather not mention. His first day of school he meets Mina Medellin - the town outcast. Not only does she wear black clothes and practice henna on herself, she's been known to beat up the strongest, most popular guys in school. Partnered up on a project about Halley's Comet, the attraction is obvious between them, but is heightened when Nick discovers journals in his attic bedroom written by his dead uncle that describe ghosts and monsters along with a magical pen and sword. While observing Halley‘s comet one night at Chatfield Hollow, Nick and Mina run into Hank Kelsey, a Werepig who inadvertently leads them to the pen and the sword. The pen lets Nick write down everything he sees in the supernatural world, and the sword releases the strength in Mina to protect them while they explore this new world they can see. With that in mind, Nick does his best to be a regular kid - he joins the baseball team all while seeing more and more of the supernatural world. Mina dives head first into training after meeting Gertrude - a ninety year old woman with powers similar to hers. But how can you be a regular teenager when you’re chasing vampires, werewolves, zombies, and you see ghosts in the locker room?