One idea could be a crossover with 'Sword Art Online'. The Goblin Slayer could be transported into the virtual world of SAO where he has to deal with goblin - like mobs in a different gaming environment. He might use his unique skills and no - nonsense attitude to clear floors and quests in the game.
One interesting aspect could be the contrast in their fighting styles. The Goblin Slayer is more methodical and strategic when dealing with goblins, using his knowledge of their habits. The Doom Slayer, on the other hand, is a force of pure destruction. In a crossover, perhaps they could learn from each other. The Goblin Slayer could pick up some of the Doom Slayer's more aggressive tactics, while the Doom Slayer might gain some strategic thinking from the Goblin Slayer.
In a crossover with 'Fullmetal Alchemist', Edward Elric could be an interesting addition. His knowledge of alchemy and his quest for the Philosopher's Stone could intersect with the Goblin Slayer's world in unexpected ways. From Goblin Slayer, Dwarf Shaman could be included. His knowledge of runes and magic could complement Edward's alchemical skills, and their interactions would be full of banter and learning.
There could be a cultural clash. The Doom Slayer comes from a more futuristic and hellish setting, while the Goblin Slayer is in a medieval - ish fantasy world. Their ways of communicating and understanding the world are different. However, this could also lead to some interesting exchanges. For example, the Goblin Slayer might be fascinated by the Doom Slayer's energy - based weapons, and the Doom Slayer could be intrigued by the magic and alchemy in the Goblin Slayer's world.
For a Goblin Slayer crossover fanfiction, consider a crossover with 'Harry Potter'. The Goblin Slayer could be transported to the wizarding world. He would be confused by the magic there at first, but then realize that goblins also exist in this world. He could team up with Harry and his friends to stop a goblin - related dark magic plot. This would bring a unique mix of the gritty, down - to - earth fighting style of the Goblin Slayer with the magical world of 'Harry Potter'.
How about a crossover with 'Fairy Tail'? The Goblin Slayer's serious and methodical approach to slaying goblins could contrast with the more flamboyant and magic - using mages of Fairy Tail. They could team up to fight goblins that have been magically enhanced or are causing trouble in the Fairy Tail world.
One possible plot could be that the Doom Slayer is somehow transported to the world of Goblin Slayer. He then teams up with Goblin Slayer to take on an especially powerful horde of goblins that have been corrupted by demonic forces from Doom. Their combined skills in combat, the Doom Slayer's superhuman strength and arsenal, and Goblin Slayer's knowledge of goblin tactics would make for an epic battle.
A crossover storyline could involve Naruto's world being invaded by goblins. Naruto and his friends would have to use their ninja skills to fight the goblins. For example, Naruto could use his shadow clones to overwhelm the goblins while Sasuke uses his Sharingan to predict their moves. The Goblin Slayer could then arrive in the Naruto world, perhaps through a strange portal. He would be shocked by the new types of enemies but would quickly adapt his goblin - slaying techniques. Together, they would form an unlikely alliance to take on the goblin threat and protect both worlds.
One possible plot could be that the Doom Slayer somehow gets transported to the world of Goblin Slayer. He then uses his advanced weaponry and combat skills to help the Goblin Slayer in his never - ending fight against the goblins. Maybe they team up to take on a super - powerful goblin boss that neither could defeat alone.