Loki approached Heimdall on the rainbow bridge. Loki's movements were calm as he walked, though from afar, Heimdall could see the small twitches on his face, the tell-tale tightness of his mouth. Something was going to happen and they both knew it.
"Tell me Loki, how did you get the Jotuns into Asgard?" Heimdall asked as Loki halted in front of him with Gungnir in his hand.
"Do you think the Bifrost is the only way in and out of this realm? There are secret paths between the worlds to which to you, with all your gifts, are blind. But I have need of them no longer, now that I'm king. And I say for your act of treason, you are relieved of your duties as gatekeeper and no longer citizen of Asgard!" Loki talked quickly without blinking. The frustration in his voice was evident, as if this was something he had ached to tell Heimdall for a long time mixed by the betrayal of letting the Warriors three and Sif join Thor on Earth.
"Then I need no longer obey you." Heimdall answered promptly, before he drew his sword in haste.
But just as quickly as Heimdall swung his sword, Loki had drawn a blue casket, that seemed to freeze Heimdall on the spot, letting Gungnir fall to the ground. Time was of the essence as Heimdall felt the cold creep underneath his armor, numbed his skin, and froze him to the very core. Heimdall mustered all his powers in one powerful swing in a last ditch attempt to stop Loki.
Before Heimdall had registered what had happened, he had cut Loki's head clean off.
Heimdall fell, knee-first to the ground, shivering from the cold. He managed to catch a glimpse of Loki's skin fading from blue to his normal self as the Casket slipped out of his fingers, before Heimdall saw no more as he closed his eyes and tried to regain some warmth by hugging himself.
Heimdall stayed like that for a while, numb and unthinking. It was nice in a way. As brief as the moment may be, Heimdall was no longer Heimdall, he wasn't the gatekeeper, and he didn't have the ability to see and hear all. He stayed like that for a while.
That was until he opened his eyes and stared right into Loki's wide, unseeing gaze.
Loki's lips were slightly parted, and his facial expression appeared as if in shock. It was incredibly unflattering on the normally attractive face. Not only that, his whole head had been severed from his body which lied awkwardly on the ground.
After Heimdall was no longer cold, he stood up and looked at what he had done.
Now what?
Even if what Loki had done was a crime; letting the Jotuns into Asgard, it wasn't Heimdall's place to act as the judge nor the executioner. What Heimdall had done could never be undone. How would Thor react when he returned and found his brother dead? How would Odin sentence Heimdall? What about Frigga?
Heimdall's heart dropped at the thought of Frigga. He imagined her reaction. How she would grieve and mourn. Heimdall was never really fond of Loki, but his affection for his mother was genuine, and Frigga's love towards her son was true. For a moment the no longer gatekeeper was overtaken by sadness.
He couldn't bear to think about Frigga anymore. He wouldn't be able to bear passing the news of Frigga's youngest son's death to her.
Heimdall couldn't quite explain his next action. He pushed Loki's body towards the edge of the rainbow bridge with his feet. Without ceremony, Loki's body simply fell into the nothingness, and the abyss swallowed his body and left no trace. He was about to do the same with Loki's head, but instead he picked it up.
He looked at Loki's face a last time, and into Loki's staring eyes.
What had possessed Loki to let the Jotuns into Asgard? To send the Destroyer after Thor? What was his motivations?
"I guess your secrets die with you." Heimdall mumbled before he dropped Loki's head.