Forged in Fire: Bringer of Chaos
Universal book link (find it anywhere available) https://books2read.com/u/bpW7Kg

Books in this series include Origin of Pietas, and Lights Out. Links below.

Six slid their canteen off over his head and held it out to Pietas.
Accepting anything from a human, an altered one at that, had violated every instinct at first. To take from an enemy, yes. Always. Let one give you something as if you needed it? Admit a weakness before an enemy?
Never.
But this was Six.
Pietas took it.
Ultras could go days without water, but they consumed it when they had it. He wiped one dusty hand across his mouth. The satisfaction of assuaged thirst never failed to please. What simple things in life brought pleasure! In captivity, he'd dreamed of even a drop to cool his tongue. He'd sworn he'd never take water for granted again.
Six had offered it to their companions during the climb, but the entire lot refused anything a mortal's lips had touched. Yes, Six was a quasi-immortal. A dead human soldier who'd been resurrected and enhanced with Ultra blood. A "ghost." But to the others, that gave him even less status.
Pietas wavered on few things, but on this? Should he call the man human, mortal, quasi-immortal, or ghost? He'd elected to choose as the mood struck. But one in particular annoyed Six.
"Thanks, ghost." He thrust the canteen against Six's chest.
Staggering, he swore in Spanish. "Find another name for me."
"Tell me your mortal name then."
"You know I can't." Six scratched his cheek. "Gotta protect my family. If your kind knew who they were, they'd slaughter them. You wouldn't, but them?"
Now they were getting somewhere. "So you do trust me?"
"Pi, there's more honor in your left big toe than your entire race combined." He tipped up the canteen but then paused. "No offense."
"None taken. But we're stranded, my friend. Unless a miracle happens, by the time we get off this world, your family will be long dead." He added, "No offense."
Six finished his drink and plugged the canteen. "None taken. Sorry. Can't do it." He lifted the strap back over his head and settled it onto his shoulder, the canteen at his back. "Seriously, Pi, your people hear you call me you-know-what, it'll give away I was Ghost Corps. We both know what they'll do to me."

Video for Bringer of Chaos

Who Are the Ultras featuring Nik Nitsvetov as Pietas
Voiceover performed by Zack Black
Images courtesy of: Depositphotos.com, Nik Nitsvetov and @by_cosphoto
Charon's Boat image custom designed by Nano-Core for the series
Video editor Zealot6 (fiverr.com/zealot6)
Based on the Sci Fi series Bringer of Chaos by Kayelle Allen
Music: Dreams of War by Orchestralis, licensed via Dual Horns Studios Ltd