Not necessarily. There are many fictional characters with incredibly powerful abilities and it's hard to say for sure if Doom Slayer is the absolute strongest.
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.
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.
Well, the Doom Slayer's origin lies in a not - so - distant future. He was a part of the military stationed on Mars. The UAC's actions in exploring the unknown and trying to harness energy from other dimensions were the catalysts. They accidentally opened the gates to Hell. Our future marine was then thrust into a world of nightmares. Demons flooded in, and he was one of the few who didn't cower. Instead, he fought back with everything he had. His origin story is about a man pushed to the brink of insanity by the horrors of Hell but finding the strength within to become a slayer of demons. He has since been on an eternal quest to purge the universe of these demonic threats.
Well, some Olympians might be offended. In God of War, the portrayals of the gods are often rather violent and not in line with their traditional, more glorified images. For example, Zeus is shown as a rather tyrannical figure in the game, and in fanfiction that might be even more exaggerated. So they might not be too happy about it.
One of the key elements is his human origin. He was just a normal man before the disaster. The UAC's irresponsible scientific exploration that led to the connection with Hell is another important part. And of course, his decision to fight back against the demons instead of running away. This shows his courage and the birth of his new identity as the Doom Slayer. His experiences of seeing the destruction and death caused by the demons are what shaped his unending rage towards them.
The fanfiction might also play with the idea of redemption for the female demon. Since the Doom Slayer is often associated with justice, perhaps he sees some potential in her to change. It could be a story of her trying to break free from her demonic nature with the help of the Doom Slayer. Their relationship could develop from pure enmity to something more complex, like an unlikely alliance or even a romantic connection in a more extreme take on the story.
Well, 'Doom Slayer: Redemption' is a great fanfic. It shows the Slayer's struggle with his own inner demons while still fighting the literal demons. Then there's 'The Doom Slayer's Allies'. This fanfic explores the relationships the Slayer could have with other characters, whether they be human survivors or other powerful entities. And don't forget about 'Doom Slayer: In the Wasteland'. It's set in a post - apocalyptic world where the Slayer has to face not only demons but also the harsh environment.
Definitely the Emperor of Mankind. The contrast between the all - seeing, all - powerful (sort of) Emperor and the single - minded, brutally efficient Doom Slayer would be fascinating. They could have a complex relationship, with the Emperor trying to direct the Slayer's rage for the 'greater good' of the Warhammer universe.
One possible plot could be that Natsu discovers his new power as a war god slayer magic user. He then has to face a series of powerful enemies who are threatening the world. Along the way, he might meet new allies who also have unique magic abilities. As he battles these foes, he gradually masters his war god slayer magic and becomes a more powerful wizard.