Many survivors endured through sheer willpower. For example, those in concentration camps during World War II. They held onto the hope of seeing their families again or the end of the war. Some would share what little food they had, creating a sense of community that helped them survive.
His best friend from before the war could be a main character. This friend might have been waiting for Ash's return and now has to deal with the changed Ash.
A compelling plot that keeps readers engaged is key. Also, well-developed characters that people can relate to or find interesting make a big difference.
She could be overjoyed at first. After all, she might have been worried sick about him during the war. However, she may also be a bit hesitant. The war could have changed Ash in ways she doesn't understand yet.
Well, often it's the universal themes. For example, in 'Pride and Prejudice', the themes of love, class, and first impressions are things that people can relate to in any era.
I recommend "Run, there's something wrong with the Host." The female protagonist traveled through various small worlds to help the protagonists who were attacked by the cannon fodder of the supporting characters and save the small worlds that were in danger of being extracted. In one of the worlds, the female protagonist liked a boy who looked like the school hunk. During a class, their bodies reacted, but the male protagonist couldn't, but the female protagonist could. I hope you like this fairy's recommendation. Muah ~😗