If this is in a fictional world with agents, secrecy might be a key element. Grant Ward might have to keep his relationship a secret from his superiors or colleagues. Another element could be trust. Given the nature of his work, building and maintaining trust with his love interest would be crucial. Also, there could be a theme of sacrifice, where he has to choose between his love and his duties as an agent.
As I don't know the specific story, I can't say for sure. But common key elements in a love story could be the meeting of the two characters, the development of feelings, and some sort of conflict that challenges their relationship.
In the Agent Grant Ward love story, one key element could be the power dynamics. If he is in a hierarchical organization, his relationship might be affected by the power differences between him and his love interest or between their respective positions in the agency. Another important aspect could be the character development of Grant Ward through the love story. His experiences in love could shape his values, his loyalties, and his overall personality.