I think there’s two may ways this will go:
1. Luffy will fight with a spear and sword against Kaido.
- Luffy is holding a spear of lightning in the last panel of last chapter so it’s likely he’ll use the massive sword of Onigashima next time he uses gum gum giant.
2. The spear and sword signify Sanji and Zoro
- Zoro is the future worlds greatest swordsman and his skill with the sword is unmatched in the crew and most places in the world
- Sanjis biological father is best known for his skill with his spear and his adoptive father stated that the greatest power is the “Spear of Grit”