Random individual songs of war headcanons
King Pyus is Ingressus's great great great great great great great uncle twice removed (this goes together with my headcanon that Voltaris are related to the nether)
Thallouse's situation was similar to Senn's, obviously without being half Voltaris. His parents were killed when he was young, and Osivian's family took care of him and his surviving siblings at the time.
Thallouse, when he killed Ingressus's father, wasn't much older than him. Like 10-20 years older, and in Ardoni years that isn't much.
Related to my head canon that Nestoris have feathers upon getting inaugurated and by friends/family, the master obviously have Ingressus feathers when he was disguise as a Nestoris, but Achillean also gave him some after he was comfortable with him. Ingressus kept those feathers even after everything, he just didn't wear them. Tho after he killed Achillean he started to wear them again
Some courtesy of my pookie
Senn is 14-16, but in Ardoi age that's like 50-60
When Senn becomes an adult, he gains Thallouse's narrator voice (to add on that, I think he would also re-tell Thallouse's story's to the younger Ardoi)
Senn and Ria have full brawls over food (also Senn is very much younger brother coated)
OMG, EDIT:
I'm not sure if it's canon, but Tygren I noticed seems to prefer is left hand. So I headcanon that he's either left-handed or ambidextrous (leaning to left-handed and is just forced to use his right hand just because of how his sword is)