In some fanfictions, he might find it in an ancient weapon stash hidden in a mythical location. Maybe while on a quest, he stumbles upon a secret chamber where the katana is kept as a powerful relic from an old civilization.
It might have the ability to absorb and redirect magic. If an enemy casts a spell at Percy, the katana could absorb the magic and then send it back at the attacker, amplified. This would give Percy an edge in battles against magic - using enemies, as he could turn their own magic against them with the help of the katana.
Yes, in some fanfictions, Percy might be depicted using a katana. Fanfiction authors often like to give characters new weapons or abilities for creative and unique storylines.
Well, in some fanfictions, Percy might obtain the spear as a gift from a minor god who sees his potential. For example, a god of an ancient and forgotten war cult could give it to him, seeing Percy as a worthy warrior to carry on their legacy.
In some fanfictions, Percy might obtain the trident through a special quest. Maybe he has to prove himself worthy to an ancient sea deity who then bestows the trident upon him as a symbol of power and trust.
In fanfiction, if Percy Jackson uses Mjolnir, it could lead to some really interesting power combinations. Percy already has his water - based powers from being a son of Poseidon. Mjolnir gives the power of thunder and is a symbol of Thor's might. Percy might be able to use the hammer to control storms in a different way, perhaps combining water and lightning to create more powerful attacks. He could also use it as a physical weapon, which would be a change from his usual sword, Riptide.
Well, he might become an even more formidable wizard - warrior. The katana's swift and deadly nature could add a new dimension to his combat skills. He could use magic to enhance the katana's strikes, like making it cut through magical shields more easily.
In Percy Jackson fanfiction, monofilament wires could be used by demigods for various purposes. For example, they might be used to set up traps in the Labyrinth. Since the Labyrinth is full of twists and turns and dangerous creatures, a thin and nearly invisible monofilament wire could be strung across passages to trip up or snare monsters. Another use could be in creating improvised weapons. A demigod with a creative mind might attach a small blade to the end of a monofilament wire and use it as a sort of whip - like weapon, taking advantage of the wire's strength and flexibility.
It could have the ability to control water, like Percy's sword Riptide. Since Percy has a strong connection to water, the spear might be enchanted to work in harmony with his powers. For example, he could make the spear shoot out jets of water at his enemies.