THIS IS MOST LIKELY ONLY ONE PART BUT YOU NEED TO HEAR MY HEADCANNON!!!
Seeing as William hates unpaid overtime it made sense to me that William would hate tax. He hates the idea of working hard for money he has to give away. He gets so angry that one day he decides to research tax fraud. Grell helps him research it until a cleverly crafted plan has been created. William keeps this up for a few years with the help of Grell. Eventually, William gets caught doing tax fraud. He unfortunately gets alot of jail time. Grell doesn't agree with this and breaks him out like the girlboss she is.
Thanks for listening luv ya.