Ring of Spell Storing (minor) with Mythic spell.

[Barstro]

Haste;
sorcerer/wizard 3,

Mythic Spells in Magic Items: Mythic spells can't be crafted into magic items unless the item is an artifact (for example, you can't brew a potion of mythic cure light wounds).
Emphasis added


If you know the mythic version of a spell, any time you cast the spell, you may expend one use of mythic power to convert the spell into its mythic version as you cast it. This doesn't change the level of the spell slot you use to cast the spell.
Emphasis added


Ring of Spell Storing, Minor;
As the ring of spell storing, except it holds up to 3 levels of spells.

Can a caster store Mythic Haste into a Ring of Spell Storing (Minor) so that another character can cast it?

[Zanos]

You probably also want the ring of spell storing text here:

A spellcaster can cast any spells into the ring, so long as the total spell levels do not add up to more than 5.
It looks like spells are explicitly cast into the ring, so I don't see why you wouldn't be able to use mythic power to modify the casting going into the ring.

[Barstro]

You probably also want the ring of spell storing text here:
Probably. But I'll leave it how it was to memorialize my faults.

It looks like spells are explicitly cast into the ring, so I don't see why you wouldn't be able to use mythic power to modify the casting going into the ring.
That's my thought as well, I just want to see if there are any decent arguments against it.

[Nodicerice]

It's kind of dm discretion I'd say.

One one hand mythic magic states tou cannot craft mythic into items except artifacts but you aren't crafting with the ring. Although the ring states it stores via casting arcane or divine spells. And on e imbued with mythic power it becomes open for debate. A mythic spell is technically that, mythic, not Divine or Arcane, so...theres that

[Psychoalpha]

It's kind of dm discretion I'd say.

One one hand mythic magic states tou cannot craft mythic into items except artifacts but you aren't crafting with the ring. Although the ring states it stores via casting arcane or divine spells. And on e imbued with mythic power it becomes open for debate. A mythic spell is technically that, mythic, not Divine or Arcane, so...theres that

I don't see anything that indicates the spells are neither Divine or Arcane in the Mythic Magic write up. A spell being Divine or Arcane is an explicit thing that interacts with other rules (usually anti-magic zones specific to Divine or Arcane, specific Counterspell abilities, etc), and the Mythic Magic description says nothing about a spell changes unless specified, so it's probably more accurate to say that they are still Divine or Arcane spells charged with mythic power.

As a more specific example of the problem your reading would create, both the Heirophant and Archmage have Path abilities that interact specifically with Arcane or Divine spells, that would suddenly cease to function with their own Mythic spellcasting, which would be... silly.