Warning! Spoilers ahead for Thor #15
In the latest issue of Marvel Comics' Thor, it seems as though the God of Thunder has given Captain America his mighty hammer for good. Recent issues of the series have seen the Odinson and new King of Asgard struggling to lift his hammer (while others have inversely had an easier time), and it looks like Thor has finally figured out the reason why. As a result, the end of the issue is pretty ambiguous about the future of Mjolnir, but it does look like Thor is choosing to leave his iconic weapon in the care of Steve Rogers himself.
Ever since Thor took the throne from his father Odin after The War of the Realms, the God of Thunder has been struggling with his temperamental hammer, running into situations more and more where the hammer has become heavier and harder to wield. However, it seems as though the Son of Odin has finally determined why that's been the case, and it has everything to do with his new status as Asgard's king. While Mjolnir was made for Asgard's greatest and most worthy warrior, "the tip of the spear," Thor no longer fits that role now that he's ruling the kingdom.
This is why Mjolnir has been failing Thor, seeing as how there are now others who better fit that worthy warrior description. Thor shares this discovery with his good friend Captain America, who was worthy enough to wield Mjolnir even before the God of Thunder started having his issues with the hammer. However, in light of this change to his status quo, Thor does something quite surprising at the end of Thor #15 from writer Donny Cates and artist Michele Bandini: he leaves Mjolnir behind, seemingly for Rogers to take care of and potentially wield in future issues.
Thor has concluded that, in order to be Asgard's king, he can longer be its symbolic hammer, hence the reason why Mjolnir was growing heavier. While it makes sense, it's still a pretty major and significant shift for the God of Thunder, and it's going to be interesting to see what Captain America decides to do with the mighty hammer in future issues. While Thor has seemingly left it in his care, it's doubtful that Cap would actually wield it as he's done in past comics as well as in the MCU's Avengers: Endgame (unless the circumstances were incredibly dire). Instead, the more likely scenario is that Rogers will make sure it's kept safe for the time being.
In any case, a Thor without his hammer is like a Thor with a missing limb. Mjolnir is a crucial part of the Son of Odin, and one can imagine that it's going to be hard for the King of Asgard to be without it as he enters this new era where he truly embraces his role as king. While this new development certainly seems to indicate that Thor being on Asgard's throne won't last all that long before he's back to being a hero with Mjolnir, the interim is certainly going to be dynamic and entertaining. Additionally, if Captain America doesn't wield Mjolnir, will someone new lift the iconic weapon and become a new Thor in the Marvel Universe (like Jane Foster), or will the hammer just collect dust? Fans will just have to wait and see as Marvel's Thor continues.