Chapter 644: I'll be your sword. You'll be my shield.

The outcome was beneficial to all parties. 

The first party was Vincent. He gained a trustworthy shield against the discovery and spread of his secret if it was ever revealed.

The second party was Anna. She gained a powerful ally to have her back if the situation ever arose. To have a noble family, Anna can unconditionally trust that she isn't going to be betrayed, which was more valuable to her than all the riches she currently possesses.

Anna didn't have a noble family to act as her support, bound by a contract of trust similar to how their relationship was going to be bound soon. 

Anna had individuals such as Lucas and Bilka as her support, but no entire noble family was bound to help her whenever she asked.