Well, I beat the final boss in the main story for Monster Hunter 4 Ultimate. The game features more story than any previous game and I can basically confirm that this game borrowed inspiration from the anime/manga One Piece.
1. The first goal of the game is to gather a crew. The crew has a captain that is obsessed with his hat, similar to Luffy and his strawhat. The crew needs a cook, like Sanji, and a Hunter which is like having a swordsman similar to Zolo.
2. The next goal is to get a boat! Wow. How obvious can they be about the One Piece reference. A boat is one of the largets goals at the start of One Piece.
3. Next the game wants us to get the boat to fly like an airship. One Piece had an entire arc dedicated to getting the boat to fly into the sky to reach another land that few have seen. Monster Hunter 4 needs the boat to fly to reach another land that few have seen.
4. The emphasis on the Captain's "treasure" can be scene as Luffy's obsession with the One Piece. Plus, the whole game is about treasure, money, powerful creatures.
5. I recently found out that Monster Hunter 4 had event quests that reward players with Luffy's Fists and Zolo's Swords as weapons. Wow. They acknowledged One Piece and even included events for them. That seals the deal. This game is a combination of two things I love the most. ^_^
Bleck and Naraku caused so much pain because of lost love. Kikyo for Naraku and Tippi for Bleck. They were the main villains that caused the suffering of practically every character in the story and had at least disloyal minion.