One possible plot could be that Thomas Wayne somehow time - travels to the present where Bruce Wayne is Batman. Thomas could initially be shocked at how Bruce has turned out, but then come to understand his motives. He might offer some old - fashioned wisdom that helps Bruce in his fight against crime.
It could be Bruce Wayne himself. Marinette might admire his business acumen and his philanthropy work in Gotham. His mysterious persona as Batman could also be very appealing to her, especially if she has a taste for adventure and mystery.
The encounter could be filled with tension. Bruce might be angry at first, blaming Thomas for leaving him so early in life. But as they talk, they start to understand each other better. Thomas could share his own hopes and dreams for Gotham that he never got to fulfill, and Bruce could see a new side of his father. The description could include details of their body language, like Bruce clenching his fists at first and then gradually relaxing as they talk.
Often, she is depicted as being just as intelligent as the male Bruce Wayne. For example, she has a sharp mind for detective work and strategy. She might be able to quickly analyze crime scenes and figure out the motives of the villains.
One interesting scenario could be Thomas Wayne seeing Damian's combat skills and being both proud and a bit shocked. After all, Thomas may not have expected such a young and fierce fighter in the family. Another could be them having a deep conversation about family values, with Damian learning from Thomas about the Wayne legacy from its very origin.
Often, it starts with curiosity. Damian may be curious about his grandfather he never met. Thomas, on the other hand, is intrigued by this young Wayne. As they interact more, respect grows. Thomas sees Damian's potential and Damian looks up to Thomas as a part of his family's great history.