Thor's trusty hammer Mjolnir served him well over the millennia they were together. Alas, their union came to a tragic end when Thor's sister Hela shattered it in her hands, and though the thunder god was eventually able to persevere and tap into his own powers, he kinda still needs a weapon. The dual swords that he gained while in the Grandmaster's control are either just left behind on Sakaar or destroyed completely, so those are out of the question. Luckily, Marvel Comics history provides the solution.
Thanks to a photo of an Avengers: Infinity War Funko POP!, we know that Thor will soon be armed again by way of an axe called Jarnbjorn, a weapon he's possessed in the comics since he was a young god. Since an axe requires a handle, and Jarnbjorn's appears to be made of wood, it's possible that the weapon will be made in part from pieces of the lovable Guardian of the Galaxy, Groot.
We all know that when Infinity War starts, Thor will be found by the Guardians as the survivor of some epic space battle. He and the Guardians will have some time to kill before they go face off against Thanos with the earthbound Avengers, and it sounds like part of their time will involve him getting a new weapon. In the original Guardians, it's shown that it isn't too difficult to acquire pieces of Groot, whether it's Gamora slicing his arm off, or him willingly offering a flower to a young child. And since he can regrow his body over a span of time depending on the severity of the industry, offering a branch to Thor would be equivalent of cutting off a branch from a tree -- it will eventually regrow without leaving any lasting damage.
It's been said that Infinity War's evolving Groot -- now having grown into a teenager in recent years -- will find himself a mentor and someone to look to as a guiding hand. This movie is going to bring both the Avengers and the Guardians together, and the Avengers' God of Thunder will play a major role towards that. The Super Bowl promo shows Thor, Rocket and Groot together in a ship, apparently separated from the other Guardians. This would indicate that Thor is going to be Groot's chaperone during whatever excursion the three of them find themselves on, and thus the most likely candidate for the mentorship role.
Across each movie he's appeared in, Thor has won people over through his dopey charm, including those who initially were hostile towards him. Given how different he is from Groot's companions, both in powers and demeanor, it only makes sense the tree teen would idolize the Asgardian. He's probably the only person who could really relate to Groot, since he had to learn to grow up and be responsible in his origin film. And with the bonding done between god and walking tree, it's pretty likely that Groot will give Thor something he thinks will help in the fight against Thanos -- a piece of himself to use as part of Thor's axe, linking the two of them forever. And Thor being Thor, there's no way he'd turn down a gift from what's basically a 14-year-old boy with a severe case of hero worship.
Directed by Joe and Anthony Russo, Marvel’s Avengers: Infinity War stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland and Anthony Mackie. The film opens May 4, 2018.