Well, he could become corrupted. Frostmourne has a history of corrupting those who wield it. Anduin, being a paladin, his struggle between the light and the dark could be a central theme. Maybe he starts to question his beliefs in the light.
In a more complex scenario, Anduin getting Frostmourne could be part of a bigger plan by an ancient evil. He could be a pawn in a game that spans across different realms. His journey with Frostmourne could lead to unexpected alliances and betrayals as he tries to come to terms with the power he now wields and the destiny that seems to befall him.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3). There are often a plethora of Warcraft - related fanfictions there. Just use the search bar and type in 'Anduin Gets Frostmourne' and it should bring up relevant stories.
Naruto could be initially attracted to Frostmourne's power. He might touch it and start to feel a strange connection, but then quickly realizes the danger it poses.
One character that would be fascinating is Medivh. As a powerful mage with knowledge of time and magic, he could either be a helper or a hindrance to Anduin. He might know secrets about the time travel that Anduin is doing and use it to his own ends. Another interesting addition could be Illidan Stormrage. His complex relationship with power and his own past actions could make for some intense interactions with Anduin as he travels through time.
Well, it could mean that Percy is about to face some really dark and powerful forces. Since Frostmourne is a very significant and often evil - associated item in its original context. Maybe Percy will struggle with the corrupting influence of the sword.
Well, in the fanfiction, Draco might be publicly shamed by the Howler. It could reveal some secrets he's been hiding, like his true feelings about his family's actions in the wizarding world. Maybe it scolds him for not living up to the pure - blood expectations.
If Naruto gets the Byakugan in the fanfiction, it would be a game - changer. Firstly, his training would take a different turn as he'd need to master the Byakugan's capabilities. He could use it to predict his enemies' moves more accurately. In team battles, he'd be able to provide more detailed information about the enemy's positions and weaknesses. This new power could also make him a target for those who fear his growing strength, leading to new and exciting plot twists.
In a 'sakura gets poisoned' fanfiction, she might first start to feel unwell, like having dizziness and weakness. Her friends could then notice the strange symptoms and start to search for a cure.
Well, in this fanfiction, Deeks might face a physical attack from an unknown assailant. Maybe it's someone from his past, like an old enemy he made during one of his cases. He could get injured badly and have to rely on his friends and colleagues to help him out.
In such a fanfiction, Tails might be kidnapped by an old enemy like Dr. Eggman. His friends, like Sonic, would then start a rescue mission. They would search all over the place, from the Green Hill Zone to Eggman's secret bases.
In the 'Remus gets a Howler' fanfiction, the Howler could be a misdirected one. It was actually meant for someone else but got sent to Remus by mistake. This could lead to all sorts of comical situations as Remus tries to figure out what to do with it. He might initially think he's in trouble for something he didn't do and start to worry. Then, when he discovers it's a mistake, he has to find a way to return it to the right person without getting into more trouble himself.