Dowatchawannado
What if Twilight had a daughter and a wife, and actually had a family outside of his spy life. But then in this AU unfortunately (somehow) the word got out to his enemies and they all targeted both the daughter and his wife. The enemies were able to kill the mother but didn't get a change to with the daughter. When Twilight finally arrived at the scene of his dead wife and crying 2 year old daughter he felt a tremendous amount of guilt, knowing what had most likely happened.
After seeing the error in his mistakes he left his daughter in the hands of his sister in-law and father in-law. Time skip to about 8 years later and he receives Operation: Strix, though instead of the headquarters making him adopt a child they make him use his old alias of Loid Forger. Using this alias meant he would have to drag his bio-daughter into this mission, though it might be a little harder than he thinks to get the girl to trust him again. Especially when she can see through almost all his lies.
This story is mainly about restoring the bond between Twilight and his daughter, rather than him having a love interest.
*Note: I do not own any of the Spy x Family character they belong to Tatsuya Endo. This piece of fanfiction does not follow the anime/manga plot, so no spoilers.*