There were a few interstellar novels about the male protagonist being a soldier that could be recommended. The first book was "The Number One Mecha Warrior in the Galaxy", written by Mo Wo Ken Gu. This was a sci-fi space/ancient martial arts mecha novel, and the male lead was Edward. The second book was "The Age of the Universe", written by Zhttty. The main character was a retired special forces soldier. The third book was The First Battlefield Commander! The author was Tuige, and the male lead was a general who had won in a row. These novels all involved interstellar backgrounds and soldier characters. They could be recommended as interstellar novels with soldiers as the male lead.
He could interact in a protective way. For example, if it's a small animal like a rabbit, he might build a safe place for it. His military training would make him good at creating a secure environment.
For 'dark winter soldier fanfiction', Falcon could be an interesting character to pair with the Winter Soldier. Falcon has his own set of skills and a strong moral compass. He could help the Winter Soldier navigate the modern world and his newfound freedom. Also, Scarlet Witch would be a fascinating pairing. She could potentially help him deal with his traumatic memories through her powers. And Bucky could also be paired with Doctor Strange. Strange could use his magic to help Bucky understand and control the dark forces within him.
The Winter Soldier is none other than Bucky Barnes. His transformation into this role was a result of manipulation and experimentation. Despite his past actions, he later strives for redemption and works to atone for his deeds.