One possible theme is sacrifice. Soldiers sacrifice their time with family during Christmas for the greater good.
The theme of hope is also likely. Despite the difficult situation, soldiers hope for peace, for an end to the war, and to be reunited with their families. Christmas, with all its connotations of new beginnings and joy, can be a time when this hope is especially strong in a soldier's heart.
It might be about a soldier missing home during Christmas and reminiscing about past celebrations with family.
One possible theme is sacrifice. The soldier may have to sacrifice his time with his loved one for his duty. Another theme could be loyalty, both to his country and to his partner.
Love could be a theme. The love between the soldier and the girl, and how they maintain their relationship despite the challenges of military life.
Another theme could be courage. The girl might show courage in waiting for the soldier and facing the uncertainties of his military life.
Themes such as perseverance and courage could be in the story. The girl needs to persevere through the long periods of separation. She has to be courageous in facing the possibility of losing the soldier in combat. And there might also be a theme of patriotism, as the soldier is serving his country and the girl may support him in that noble cause.
One possible theme could be the transition from a life of military combat to a pursuit of the supernatural. Another theme might be the exploration of the unknown, as the soldier leaves behind the familiar world of the military to face the mysteries of ghosts.
One common theme is homesickness. Soldiers often miss their families during Christmas. Another is camaraderie. They rely on their fellow soldiers to create a Christmas spirit. For example, they might decorate together or share stories.
One possible theme could be family. Christmas is often a time when families come together, and the story might explore the relationships within a family during this festive season.
Survival can also be a theme. In the military environment, especially in combat situations, the soldier has to fight for his own survival. He needs to use his skills, knowledge, and instincts to stay alive. This could be a major part of the 'first soldier story', as he overcomes various threats and challenges to survive and complete his mission.
Another theme could be the celebration of faith. If Matthew is religious, his Christmas story could revolve around the religious significance of Christmas, such as attending church services, praying, and reflecting on the birth of Jesus. This would add a spiritual dimension to his Christmas story.