There is always signs.
Sirius was acting weird. Not a good weird, he would rarely talk to James, or even Remus and Peter. It was unsettling, his person who always listened and made time, never listened or had time anymore. It felt like his chest was constricting.
James tried to catch Sirius anytime he saw the Black, weather it be during meals, classes, at the dorm, or in the hall. He tried everything and Sirius always found a way to avoid, ignore, or change the subject. It upset James to no end, why wasn't he talking to him?
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Remus could see the signs, the limping, the wincing when Sirius bumped into someone, avoiding his friends. He saw the signs, he didn't know what to do. The very clear signs Sirius was in pain, he saw it and didn't do anything, cowardly really but what could he have done at 12?
He could tell someone, anyone. But he would be proven wrong, Remus had a good nose due to being a werewolf. He could smell the blood but also Sirius' magic, he could smell the pain potions Sirius took at night even in his sleep.
Remus will never forget the first time he caught a glimpse of Sirius when his glamour was down.
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Eventually Sirius stopped avoiding them as much, he slowly started coming back to them, he talked more and more everyday and didn't go out of his way to avoid him. Then he started hanging out with them again, walking every where with them again.
Remus forgot about the whole glamour thing since Sirius stopped limping and wincing and avoiding them. A stupid thing to forget.
James didn't see the signs, so he just thought Sirius had a bad argument with his parents. James couldn't smell the magic or blood like Remus could, he didn't see the signs because he wasn't accustomed to that knowledge. Remus was, he'd been in the same pain Sirius was at one point, just not for the same reasons like he thought. The real reason that he would find out later would horrify him.
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When James and Peter found about Remus' little monthly problem, they reacted much like Sirius. They were calm and said they didn't care if he was a werewolf or a fucking god he was still Remus. Though finding about his problem and considering his last name led to a nickname, Moony.
In all honesty, Remus loved it. He doesn't remember the nicknames his mother, Hope, called him. Moony, made him feel warm and cared for enough to be given a nickname. It was better then what the Slytherins called him.
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When Sirius brought up the idea of being an animagus in 2nd year Peter almost smacked him upside the head for such a stupid idea. Becoming an animagus unregistered at this age was downright stupid, it really was, but it was for Moony.
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Sirius brought up the idea around the end of 2nd year, they decided right after they got the results for their final exams back that they would go through with it. They decided they would get as much research as possible to pull it off correctly.
They researched constantly, well mainly Sirius and Peter, James was a good distraction for Remus. It was around the end of 3rd year when they had read every book on animagus's and how to become one and then read them all again to be sure. They decided who got which ingredients during the summer and which ones they'd have to get next school year.
All 3 of them planned everything to the last strand of hairs on their head. They were discreet and Remus didn't suspect a single thing to their relief. Now they just had to wait till next September 1st to go over everything.
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When they got on the express the signs were less. Like Sirius was trying to not shut them out. Remus was just glad that Sirius was trying that he didn't notice any other signs at the time.
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Everything was planned and well thought out when they finally got the last ingredient by January. They did everything according to their research. It was a hard and long process and they were not fond of having a mandrake leaf in their mouth for a month but they made it work.
They have the vial, they added the leaf, they added the teaspoon of dew, they added the crystal of Death's head hawk moth, they said the incantation every sunrise and sunset and will continue. They did everything as told, now they just had to wait till the next lightning storm. Which just happened to be in July, weird but they went with it.
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Sirius had to force himself to be calm as to not get overly excited. Sneaking out was easy, getting to the place he hid the vial was a bit harder. He had to hide it very very well because of his family, it didn't help that he had started rebelling more openly so his legs hurt a lot more. He ignored the pain.
He snuck out, got his vial, had his want at the ready pointing at his heart and repeated the same incantation he had for what felt like forever now.
"Amato Animo Animato Animagus" He said, and that's went the searing pain started. The pain spread through his whole body yet not the worst pain he's felt.
And then he heard it, the second heartbeat that felt like it was pounding right out of his chest right next to his own. He desperately wanted to know what his animagus was but James, Patrick- Peter, and him all agreed to wait untill they were all back together again.