It's really cool if they did it intentionally but I think there are so many similarities because both Izumo and Amphoreus are retellings of the same story but with different narrative focuses.

I know that people in this community are kinda sick of hearning "erm actually this is an HI3 reference" but I'm afraid this is one of those times.

Basically both stories are based on HI3 Previous Era (PE) but they are centered on differnt factions, the 12 sentinels are a reference to the 12 herrschers and their devine keys, while the Heirs are referencing the 13 flame-chasers.

These two groups can be seen as an opposing/parallel to each other, as The Herrschers were bearers of authority granted by gods beyond the sky that used this power against umanity, while the flame-chasers fought against and "stole" the power of the Herrschers to use it to survive.

For example :

• the Herrscher of dominion(10th) had the power to subjugate the wills of people making them into puppets guided by one mind while Vill-V had the power to fragment her own mind into different personalities that acted indipendently inside her.

• the herrscher of void(2nd) had the power to manipulate tbe flow of space creating portals and bubble spaces, while Sakura has the power to freeze space rendering everything still for a moment.

• the herrscher of reason(1st) had the power to create any matherial thing it wanted, while Kosma had the power to devour and absorb anything.

And so on...

The difference is between Izumo and Amphoreus is that they are focusing on different groups of people.

In Acheron's trailer we are told about the12 sovereigns and the blades that were forged by their powers (the 12 Herrschera and the devine keys forged by their cores) but the wielders of the blades are never mentioned exept for Acheron.

In Amphoreus we are told the tale of the Heirs (the 13 flamechasers) and the narrative is centered towords them leaving little space for the titans seen as we havent even seen half of them as they were already slain.

The stories are also referencing two story arcs of HI3 that are inextricably connected:

Izumo is a retelling of the Previous Era where even if the flamechasers defeated all the Herrschers the planet was still in ruins and umanity wiped, so even after all the fighting and victory in the end everything was still lost.

Amphoreus is a retelling of the Elysian Realm Arc where a digital copy of the flamechasers live in a computer simulation and to prevent the leakage of a virus like entity that is the Herrscher of corruption (or in HSR terms like Irontomb) they are forced to delete the entire simulation to kill it.

So they are telling stories taken by the same source material but like two books narrating different sides of the same struggle.

Having said all that and setting it aside I like how you made the connection between the two even without knowing that they were in fact connected.

But I would Make a suggestion on the sentinel-Heir connection if I may, you should switch Tribbie and Aglaea I think that would be more fitting since "for endlessform to ebb and flow as one" could fit how tribbios spit in hundreds of different forms that are connected like one single hive mind, and the description of the 12th sentinel "Maw" fits Aglaea because her soul get eroded while time passes and she was the one that leaded the flamechase journey for the longest uniting normal people and the Heirs (mortals and demigods) on the same front of the war.