Although Thor does believe his brother’s revelation to be genuine (particularly given the underhanded way Loki had gone about it - if it had been stated in a straightforward manner Thor likely would have assumed that Loki was back to his old intricate plans), he is at heart a man of action. Words never have quite the same effect on him as a living demonstration.
It is this tendency that he blames for his inability to leave his brother to his own devices. Although he trusts that Loki is no longer in danger, he still finds himself checking in on him as often as he ever did. In fact, it is not until several days after their conversation that Thor allows himself to truly believe that Loki is firmly on the mend.
The Avengers are sent out to combat a rampaging creature set loose in the southern part of the city. It is a massive beast, and composed of a strange material that does not seem quite natural. It easily absorbs Thor’s strikes and Tony’s repulsor blasts and nearly succeeds in swallowing Steve’s shield before Tony manages to rescue it. The creature bats him against a building for his efforts, burying him in rubble.
The team can hear Tony swearing, so they know he is unharmed even if he is incapacitated. Clearly a mightier strike than usual is necessary, so remembering his victory against the ice beast on Jotunheim Thor takes to the air, confident that a large enough missile will cause more damage than the beast can deflect.
He does not get to test his theory. Before he makes it to his target the creature strikes him mightily, moving far more quickly than before. Thor tumbles to the ground, momentarily losing hold of Mjolnir as he skids across the pavement.
Winded, battered, and starting to actually worry about their chances, Thor looks up and finds himself in a crowd of Thors, all moving independently. There are copies of the other Avengers as well.
The creature roars in fury, striking at the illusions. Ice creeps up its base, covering it and holding it immobile, and well-placed explosive rounds from Natasha and Clint soon reduce it to useless fragments.
The illusions vanish. Loki turns away from the beast and stalks over to Thor, Jotun-blue fading from his face and right hand.
“Brother, that was most impressive!” Thor says happily, getting to his feet. This is the first battle Loki has been in since the fight on the Bifrost, which Thor generally tries not to think about, and it is the first time that Thor has ever seen Loki use his Jotun powers so naturally. It is a most welcome sight, and the thought that Loki must have been keeping watch over them in secret warms him.
Loki does not look nearly so jovial. “What have I told you about charging in without a plan?” he shouts, and strikes Thor in the head. “You could have been killed, you imbecile!”
“I did have a plan, brother,” Thor says mildly, rubbing his jaw. Loki still needs to build up a good deal of his lost muscle mass.
Loki makes an aggravated sound and vanishes Thor’s clothing with one hand, stomping off to help dig Tony out of the rubble.
His undressed state does not worry Thor overmuch - the fight is over, so he has no need for his armor, and he is reasonably certain his brother’s temperament will recover in time to bring it back for the next battle. In the meantime, Thor is pleased to have his brother’s cunning mind and magical skill once more at his side. It would have been very easy for him to put himself deliberately in harm’s way, and yet he had instead chosen an effective and practical method to defeat the creature.
Thor beams. He has his brother back, spiteful tricks and all.There is very little that could spoil his cheer at this moment.
“Loki,” Clint says, “Loki, please give your brother some underwear oh God my brain.”
“Is my brother not magnificent in battle?” Thor asks proudly. Steve coughs delicately and surrenders his much-abused shield to preserve Thor’s modesty.