In a past or alternate HGW, a girl summons herself an archer and does it wrong on accident, resulting in an unstable summon. The Archer in question is Gil, whose form fluctuates between ko-gil and adult self with the former being present at night and the latter in the day. Which means she has a way more tolerable partner during the wartime
The story heavily plays up/abuses the differing nature between the two and the way ko-gil messes with Gil's perspective to actually make the romance possible and also drag out the war long enough to make it feasible
All is peaches until as time goes on, the protagonist begins to wonder what they'll choose: the wish to bring back the loved one that they entered the war for, or a wish to keep her servant.
Right near the end of the war, some divine being probably ishtar shows up in one of her dreams and convinces her that he's actually the one who caused the death of her loved one in the first place in a previous war
torn by grief, she wishes for them both to die in the hope they'll be reborn another time when she'll be able to love him without guilt. She keels over and then whatever divine trickster is the cause of it shows up to gloat for a bit before he's forcibly sent back to the throne
probably ishtarshows up in one of her dreams and convinces her that he's actually the one who caused the death of her loved one in the first place in a previous war