Tadashi couldn't make himself regret trying to help Professor Callaghan; someone had to help after all. But leaving Hiro? That he regretted more than anything. Well not so much leave, Hiro just didn't know he was still here. AU where Tadashi's spirit ties itself to Baymax.

This will be a multi-chapter fic. I own nothing of Big Hero 6.

When the text is italicized Tadashi is talking, or it's a flashback.

When "parenthesis" is used Baymax is talking.

When the "italics" is in parenthesis Tadashi is talking directly through Baymax.

Prologue: Hiro

Tadashi no!

Callaghan's in there, someone has to help!

There was heat.

Then pain, a heavy feeling in his chest.

There was soot, and smoke, and fear, and he couldn't move.

And then there was nothing.

Even later, Tadashi wouldn't be able to explain what it felt like to become aware of himself again. He supposed it could be compared to the feeling of waking up from an afternoon nap. A slow, gradual process of waking that left one unaware that they were even awake until they realized they were staring up at the ceiling and had been for a while. The sense of disorientation was familiar, of being oddly disconnected from everything around him.

He'd never much liked that feeling.

Yet it was different from waking up. There was something—other about it. He felt that if he didn't concentrate his entire consciousness on simply being he'd fade away.

So he focused.

My name is Tadashi Hamada. I go to SFIT.

I have an Aunt, and friends.

And a brother, Hiro.

Hiro.

Hiro. Hiro-Hiro-hirohirohirohirohirohirohirohirohirohirohiro.

Even with the loud crackling of the flames, the incredibly loud roar of the fire, he could here feet smacking the pavement behind him.

Hiro followed me.

And it was as if this thought brought the shattered pieces back together. Tadashi knew in that moment that he was dead. There was no disbelief. No confusion.

But Hiro, his baby brother, couldn't be dead. Not Hiro.

Not Hiro, who still had so much life in him. Whose only mistake had been following his idiot brother.

Hiro can't be dead.

He felt a pull in his chest, or more his very being, and at that moment he didn't care if it took him away. As long as it took him to Hiro.

He really didn't know how he ended up at the San Fransokyo General Hospital. He didn't particularly care.

Aunt Cass was there. She was crying.

His friends sat next to her in the waiting room, Tadashi couldn't tell which waiting room it was.

His heart leapt into his throat.

Aunt Cass rose to her feet, offering the others a teary smile. Tadashi had never seen a smile so forced on his Aunt's face.

"Thanks for coming you guys. I should get back to Hiro. They had to give him something to calm him down, I don't him to wake up alone." Her voice broke halfway through. Honey Lemon pulled her into a hug, even as tears began to stream from her already red and puffy eyes.

In any other moment Tadashi would've thanked Honey, but at the moment all he could process was Hiro.

He was alive.

I want to see him.

That invisible force tugged at him again, more gently this time. Tadashi didn't fight it, this time he knew for sure that it was taking him to Hiro.

He followed the tug ahead of Aunt Cass and stood in the space between the curtains separating Hiro from the rest of what Tadashi now recognized as the emergency room.

Hiro.

"Hiro, sweetie. You're awake." Aunt Cass bustled into the room, right through Tadashi. Tadashi didn't even feel it.

"Aunt Cass, where's . . . Where's Tadashi?"

Aunt Cass was crying again.

"Sweetie—"

"He's—he's gone huh?"

"Yeah." It was a croak.

I'm not. I'm right here.

The next month went in much the same way for Tadashi.

Hiro and Aunt Cass became the thing he spent all of his time focusing on. Focusing on them just so he would have a reason to stay, to exist.

I'm scared. I don't want to leave them.

He had to live (figuratively, he thought a bit sarcastically) through his own funeral and the wake.

Professor Callaghan had died too. He hadn't even gotten much past the door before the explosion hit.

He stayed upstairs with Hiro during the wake, only drifting downstairs once or twice to catch a glimpse of his friends.

Hiro withdrew from everyone. Even Aunt Cass couldn't pull him out of it.

Tadashi knew he had to do something when Hiro threw away his acceptance letter.

He just didn't know what he could do.

Until Hiro dropped Megabot on his foot.

"Hello, I am Baymax. Your Personal Healthcare Companion."

So tell me what you thought! I know the stream of consciousness is a bit choppy, I did that on purpose because Tadashi has to pretty much be constantly focusing on something. That will change next chapter. It will also follow canon much more closely from now on, I just needed to set things up a bit first.