-Side Effects-

This is another one of my AU fic with time travel concept.

This story starts when Harry goes to Grimmauld Place after Dementor attack.

English is not my native language. So pardon me for any grammatical mistakes.

Disclaimer: HP doesn't belong to me.

"Hey Siri.. look at this." Harry called Sirius, showing one small box that he found while cleaning the cabinet. The box was completely black with small stars engraved on it. It was made of glass with a knife shaped lock in front of it.

Harry decided to help Sirius clean Black House library earlier that day. The rest of the occupants of Grimmauld Place were cleaning the upper floors.

"That's an interesting box. Where did you find it?" Sirius eyed that small box suspiciously which he had never seen before.

"Oh, I was cleaning that cabinet next to the bookshelf, and while cleaning the mirror came out, and then I found a hidden drawer with this box in it." Harry gestured towards the cabinet, where he found that small glass box. He was also inspecting that box, trying to open it.

"Harry this might be dangerous. You have seen this house is full of dark stuff. Give me that, there might be some nasty jinx on it."

Sirius tried taking that box out of Harry's hand, but cut his finger with its knife shaped lock.

As soon as his blood touched it, the box started glowing.

Sirius haphazardly took that box from out of Harry's hands, and put it on the desk.

There was a clicking sound, and the box slowly opened up.

Both moved forward to inspect its contents. There they found a small egg sized black star, appeared to be made of glass, lying on the velvety interior of the box. Then slowly, that star started rising, and once it was above their heads, a voice started coming out of it.

"You have chosen time journey to change the fate of your world. You will go where this all started, but beware there might be some side effects, as you have chosen to open black star box."

Both Harry and Sirius looked at each other, not liking the sound of what that voice just said. Immediately they moved forward to shut the box and in process Harry's glasses slid off to drop on floor. Both tried to close the box, but as soon as their hands touched it, the star burst and there was a shower of light around then.

Immediately they felt a pull and ticklish feeling throughout their bodies. The light was so bright that they could not see anything. They closed their eyes but kept on holding that box, as they could not remove their hands even when they tried to. After what felt like ages, the pull stopped. Harry was the first one to open his eyes. He found himself standing in a park. "Where?" He stopped, as a different voice came out.

He looked next to him, expecting for to see Sirius, but found a teenage boy of his age standing there. "What? Who?" Again that female voice came out.

Sirius opened his eyes next and gazed around. Then looked towards Harry, but found a girl of Harry's age standing there. She was staring at him with her green eyes, which were just like Harry's.

"Who are you? Where is Harry?" He started looking around for his godson.

The girl frowned, and said, " I am Harry. But who are you?"

Sirius stared at that girl again. Her hair were waist length, but were black just like Harry's. She was of same height as Harry. Her eyes were exactly the same but Harry's glasses were missing. Then his eyes fell on the lightning shaped scar on that girl's forehead. Then remembered what the voice coming out of that black star had said 'beware there might be some side effects'. Sirius glanced back at that girl, who just asked "What?". On hearing a girlish voice out of Harry mouth Sirius could not control and started laughing hard.

"Oh Merlin it's you Harry..hahahaha. " Sirius kept on laughing, holding his stomach.

Harry frowned at the boy who was laughing at him for some unknown reason. Getting irritated, he said, "Excuse me. But who are you?"

At this Sirius started checking his own body, praying not to be a girl like Harry. He looked at his hands, they were slightly smaller. Even his body appeared slightly shorter. He glanced back his godson, "Its me Sirius. Do I look different?" Sirius noticed that his voice sounded younger too.

Harry observed that boy who claimed himself to be Sirius. He appeared quite similar to Sirius. "What do you mean what you look like? You look like a boy. And if you are Sirius, then change yourself into your animagus form."

Suddenly, that boy changed himself into black dog, then tranformed himself back into his human form.

Harry gazed at his godfather in astonishment, "Sirius? It is you. What happened? You look like a 15 year old boy."

Sirius smiled at Harry, "Harry if you are shocked to see me. I think you will be more shocked with yourself. Just look at yourself."

Harry took out his wand, and conjured a mirror to look at himself. There in his place, was a young girl with same eyes but longer hair. Her nose, face shape and lips appeared different. Her skin looked a lot softer. He also noticed that she was not wearing any glasses. Then he glanced at her forhead, and saw lightning bolt scar. Then he realised that it was him, he was the witch in the mirror. He was now a 'she'.

With complete shock, she kept on looking back at her reflection with her mouth wide open.

Sirius just stared as his godson, who was now his goddaughter, going completely still in shock. He put his hand on her shoulder, "Harry."

Harry looked up at her godfather, "How?"

"Remember the voice that came out of that star. It said there would be side effects. I think these are the side effects of whatever this box has done." Both gazed at the black box which was lying innocently on the grass.

Harry glanced back at Sirius, "But Siri, it also said something about journey to change fate. You think this box took us somewhere else, because I felt a pull too." Harry started looking around. She also noticed that she could see clearly without her glasses. Then asked, "Do you think we are in a different country?"

They were in some park, surrounded by trees. It felt like early morning hours, as they could hear early chirping of birds.

"Harry that voice said time journey to change fate. So I don't think we are in different country. I think we are in different time. But it might not be more than a year, because it's impossible to travel back or forward through time more than that." Sirius replied, while adjusting his clothes and shoes with wand as they were quite lose for his smaller body.

"So you think I can prevent Voldemort's rebirth, or stop Crouch Jr from putting my name in Tri wizard tournament. " Harry asked excitedly.

"Let's check whats the date today. But I think we are in muggle London. But first, let me tranform your clothes. A young girl doesn't look good in thosr lose shirt and jeans. And those trainers are complete no no." Sirius responded, as he picked up the black box and pocketed it after putting shrinking charm on it.

"Okay Siri, but I don't want to wear skirts. Just make these clothes slightly fitted, like you did with yours."

Her godfather nodded and shrunk her clothes slightly, so they could fit her.

"I think we should apparate to Leaky Cauldron. Just hold my hand."

Harry held Sirius's hand, then there was a pull and she felt herself of being squeezed through rubber pipe. Once it stopped, she opened her eyes. They were standing in a dark alley.

"Its this way.", Sirius said, pulling Harry's hand. They turned right and Harry looked around muggle London. The traffic was far too less, and the vehicles looked like the ones she saw in old movies. Even people were wearing clothes like old movies.

"Sirius I think we are more than a year back." Harry said with a dreadful feeling.

"What?", Sirius stared at his goddaughter.

"Look at the type of cars on the road, and the clothes muggles are wearing." Harry said while gesturing towards a couple who they just passed.

Then Sirius also noticed, muggle London indeed looked quite different. They stopped walking and started looking around, a muggle passing by accidently knocked against Sirius's shoulder and dropped his newspaper. Harry picked it up to return, then she noticed the date.

"Thanks", muggle said while taking newspaper from Harry and moving on.

"Siri...I think we're wayyy more than a year back."

Sirius looked at Harry questionably. Harry stared at her godfather, "That was a muggle newspaper, and it said 3rd Aug 1943."