Some previous comments threw me off my immersion ffs
But these two seem to just be a pair of unfortunate souls seeking to "redeem their humanity" or something. Onee-san is looking for a new beginning, though she may not realize it yet. And Child Soldier-kun is ticking off things in his childhood bucket list that he has never been allowed to do.
In the spirit of a fresh start, these two are a splendid bunch... not to mention, kind voluptuous sister-figures are always a Godsend. 🍜✨