Iron Deficiency Anemia/ Pernicious Anemia
Loki always underestimated the fragility of Midgardians.
His boyfriend flew around in a metal suit destroying other-worldly beings, so you cannot fault him for forgetting that humans were easily breakable.
One thing Loki could never grasp his mind around was medication- pills.
He didn’t understand the concept of consuming small pods to maintain one’s health. He always forgot Midgardian bodies did not heal themselves and sometimes needed assistance to keep running.
So when he took Tony on a two week-long trip to Asgard, he totally forgot his task of reminding Tony to consume his so-called ‘pills’. It was the only job Bruce had tasked him with, knowing his boyfriend’s robot would not be accompanying them, and the genius never remembered himself.
He had noticed how tired his boyfriend had gotten, and by the end of the first week, it was rare for Tony to go a whole day without two or more naps.
They had to cancel their plans to tour the galaxy when Tony woke up with a debilitating headache.
Loki spent the day with the smaller man curled in his arms whimpering pitifully. Loki had closed all the curtains, limited noise, and layed a cool cloth over Tony’s forehead, but he continued to complain of pain.
There were other abnormal Midgardian tendencies that Loki had noticed- having studied them immensely during his travels.
Tony’s body seemed colder than normal, almost cold enough to rival his own skin. Loki covered him in as many blankets as possible, but the genius continued to shiver. His skin was paler than normal- Loki having grown fond of Tony’s olive skin. And finally, when the genius wasn’t vomiting or refusing the food the cooks brought up for him, Tony whined of a craving for dirt.
Loki never gave in because he knew dirt was not on the list of normal consumption for Midgardians, but he was incredibly perplexed.
It wasn’t until the billionaire fainted that Loki decided to cancel their trip and carry the sickly man back to Midgard. Even if it meant facing Bruce’s rath.
Loki laid Tony onto the couch just as all the Avengers gathered around. “I don’t know what’s wrong with him,” he said worriedly. “He suddenly grew ill.”
The Avengers watched silently as Bruce moved around taking Tony’s vitals. Finally he sighed, standing back. “I’ll have to do more tests in the medical wing. Steve?” Steve nodded and lifted the billionaire.
Loki watched sadly as they carried his boyfriend away. Sam noticed that sad sorcerer and put a sympathetic hand on his shoulder. “Hey man, don’t blame yourself. Tony has a lot of medical problems. So as long as you’ve followed Bruce’s suggestions, given Tony his pills, you’ve done all you can.”
Loki froze at the mention of pills. Before he could say anything Bruce’s voice came over the room’s speaker. “Hey Loki? The tests are showing Tony’s iron and B-12 levels are low. Have you been giving him his pills?”
Loki’s face colored in a blush. “Oops,” he said quickly before disappearing from the tower.