And the universe succumbs beneath his tooth and claw.

Revealing another, larger universe.

This universe is also sort of round and dark and oblong, though it is much larger.
There is an opening in the roof providing only limited light, depending on the time of day. Fortunately he can still see the whole place just fine. Very convenient.

He has therefore learnt an essential lesson. If something is bad, such as because it is not food but should be, he should get angry and attack it until it changes its mind.

This universe is also bad though, because he has now bitten as many as several things and none of them have been food.

One of them has hatched, she notices.

A red dragon has more parental instinct than the average lizard, but less than the average bird. Still, she'll toss some scraps of overcooked horse meat into the nursery chamber.

And she'll tell it, in perfectly clear Draconic, to eat.

He'd heard noises like that in the previous universe, although they sound different now that he's not swimming in food.

The monster manual might say wyrmlings can speak Draconic but they probably don't mean literally from the moment they hatch, right? It probably takes a year or two to learn, at least.

Uh, sure. Why not. You have to spend a couple years learning Draconic like anybody else would. Lets go with two years to full fluency, since you live a long time regardless but start out more intelligent and developed than a comparable human baby.

In that case, he doesn't understand it yet. He'll have to figure it out from correlations like everybody else.

This will continue for a few days, as he begins to get used to using his limbs and moving around, and his eyes learn how to recognise shapes and process them into objects.

Why did the universe stop having food? This is an outrage. It will pay for this.

She too, emerges into the bigger universe.

Oh look, more food. She should go eat it.

What new injustice is this?
Food is being brought to the universe for me to eat, as is intrinsically just.
But now this other entity, which clearly is not me, is eating the food.
This is a travesty.

Some deep instinct inside him tells him he should try his hardest to breathe at the travesty that is eating his food.

A bunch of fire comes out.

She is completely unharmed by this but on impulse and in retaliation will breathe it right back.

Then they'll both breathe fire at each other for a bit.

This isn't working. What if he tries to hit her with a claw?

As soon as you both stop breathing fire at eachother, the room returns to darkness. It doesn't matter though because you both have Darkvision and also Blindsense.

His attack: 1d20 + 11 (Claw) = 19
Her AC: 19
Hit lands.
damage: 1d4 + 3 = 7
His HP: 7d12 + 14 = 67
Her HP: 7d12 + 14 = 68 - 7 = 61

Ow. That hurts.

This is literally the worst thing that has ever happened, narrowly beating out that thing earlier where the universe ran out of food. She'll do the same thing right back.

Her attack: 1d20 + 11 (Claw) = 30
His AC: 19
Hit lands.
damage: 1d4 + 3 = 4
His HP: 67 - 4 = 63
Her HP: 61

Ow. That hurts.

Is that what he just did to her? It hurts that much? And he just did it because she wanted food, same as he did, and for no other reason?

Do siblings really need to fight each other like this? Is it not possible to do something better, kinder even?
Nah that's silly.

He'll try a bite attack.

His attack: 1d20 + 11 (Bite) = 27
Her AC: 19
Hit lands.
damage: 1d6 + 4 = 2
His HP: 63
Her HP: 61-2 = 59

Ow. Why do bad things keep happening to me.

She'll scream out in annoyance.

It's going to take a while for this to end, isn't it?

What if she tries to attack really really hard? Like, do an attack, but put all of her power into it. Like some kind of Power Attack? Maybe that'd help?

Totally a thing! It's a feat but it's a feat you have!

Great! Lets do that then! With a bite, since if her brother is using bites she'll try one too.

Her attack: 1d20 + 11 (Bite) - 1 (Power Attack) = 11
His AC: 19
It misses.

He manages to dodge out of the way. Possibly her trying to put more power into the attack made that a bit easier?

Reality has betrayed me. He was supposed to get bitten.