It crashes into the slope behind them, shaking the ground, then starts flinging itself up in their tracks.

Hashirama's most powerful attacks all rely on Mokuton, which isn't working at scale here - 

Molding the earth doesn't work, or it does in a way but feels like it'll take more energy than he has -

Sasuke shoots a fire-dragon at it.

Which washes over its skin - apparently just making it angry.

It slams into the ground again, throwing waves of sand out.

Hashirama's forced to dodge, his trajectory bringing him away from Sasuke when he miscalculates the other's path.

It twists, massive jaws - each tooth larger than his hand - gaping as it surges for him.

Its first bite destroys a hastily constructed wooden barricade grown from Hashirama's arms, the teeth snapping inches from his flesh.

He throws himself back, but he's firmly on the defensive now.

And it's faster than him as it lunges again.

Sasuke, meanwhile, has what can only be called a panic attack - he's gotten used to fighting through them, to ignoring the way his blood freezes in his veins and his thoughts shiver and scatter and circle around themselves - 

He sprints towards Hashirama, but there's an insistent screeching in his head he won't be fast enough, and a grievous burning in his eyes - 

And something unfolds around him as he imposes himself between Hashirama and the monster, his sword drawn and crackling with lightning that sparks black.

The monster's teeth close around the construct, with enough force to crumple steel - 

But Sasuke's Susano holds, and he gestures forwards, the thing's arm forming a blade of black fire and stabbing forwards and up even as he limes the entire construct with lightning.

This shark does not appreciate being suddenly electrocuted and set on ever-burning fire! It shrieks and rears back, thrashing, then turns, swimming off as rapidly as it came.

Sasuke drops the Susano and falls to his knees, gasping, vision swimming and blurring in and out, a sticky wetness on his cheeks, his sword slipping through his numb fingers.

He... Really hadn't recovered enough for that, had he.

"Shit - Sasuke!" Hashirama calls, kneeling behind him and putting his hands on his shoulders. "I got you - "

And healing chakra washes over the other boy, concentrated and tremendous, more than Hashirama's spared for healing before.

"Your eyes are bleeding..." Hashirama mutters. "Do I have your permission to try healing them?"

Sasuke's bone-deep exhaustion immediately starts receding.

"Yeah," he mutters, even as his heart races. Itachi...

Itachi had said the Mangekyou drives you blind, had attributed his black fire and Susano to it - 

Sasuke shouldn't have the Mangekyou, he didn't love Itachi, he didn't - 

(He might be hyperventilating.)

He'll frown, and consider, then slowly, giving Sasuke time to push him away, press his front to Sasuke's back, put his head on his shoulder, and just breathe deeply and evenly. 

Then of course he'll also put his hand on Sasuke's forehead, and start probing the chakra networks, blood vessels, and nerves in the optic area.

Sasuke shivers but doesn't pull away, and does, gradually, start breathing a bit better.

...Okay this is getting embarrassing but he's not sure he wants to risk disrupting the medic currently wrapping his chakra around Sasuke's eyes. Maybe just resolutely pretending this didn't happen will work...

"Your chakra networks are pretty badly inflamed," Hashirama says. "Looks like there's too much resistance and not enough capacity in them for what you were doing, causing damage, which spilled over to the blood vessels... It's also increasing pressure in your eyeballs, which if left untreated will damage your vision over time. I can relieve it, if you'd like, but it won't permanently stop that from happening again."

Sasuke half-shrugs. "Go ahead..." he mutters.

Hashirama nods and shuffles a bit, shifting his awkward sort-of-hug to relieve the building cramp in his wrist, and then gently setting about shuffling fluids and chakra around. These vessels can be knit back together, this extra fluid can be extracted, this turbulent build-up of chakra can be smoothed out and directly elsewhere, this weird and raw tangle around Sasuke's eyes - he thinks it's what's causing the problem, but he doesn't know if it's required for Sasuke's techniques to function, and he's never treated an Uchiha before healing Sasuke that first day.

Once Hashirama finishes, Sasuke disentangles himself with a muttered "Thanks" and a refusal to meet Hashirama's gaze.

"It's no problem. You saved my life with that, after all."

He doesn't push eye contact. Nor where Sasuke got that ability - it was clearly a strange eye technique, but Hashirama's never seen an Uchiha use something like that before. Of course, asking a near-stranger (no matter how much Hashirama really, really likes Sasuke) about their techniques - or even a friend or family member - is a massive taboo. 

Sasuke just shrugs, still uncomfortable and unable to bring himself to look at Hashirama. His face feels warm.

"Sorry about being kind of dead weight, there," Hashirama says after a few awkward moments of silence. "I guess I've come to rely way too much on my Mokuton and secondarily my Doton, especially against big opponents... The plants and earth here feel more resistant to my techniques, or - at least less responsive. And I'm used to drawing pretty heavily on nature chakra for just about everything..."