
He has a very low opinion of himself. His self-worth is always put into question. He had a difficult childhood. Years of holding bitter thoughts and experiences would make him disregard the importance of his own birthday and that treatment would seep to his attitude towards the birthdays of others. I'm not defending what he failed to do for Masato's birthday which is the bare minimum. I'm just trying to understand. Personally, I also don't feel like celebrating my birthdays owing to my low self-esteem.

This brief run-down is in very simple language. Hope it helps.
So the kingdom has money meant for various services to run the kingdom. But the money is not limitless, it's under a budget. The money should be used only for necessary and relevant expenses like resources for training and research. If this money runs out, the kingdom could be in serious trouble during emergencies. This money is to be managed and distributed properly by the Finance Department (where the MC works). What the main character noticed was that the Knights were applying for money even for unnecessary expenses like lavish food and brothel (sex work) services. Basically, they were misusing the kingdom's money to have fun because the Finance Department is too lenient or easy to take advantage of. The department is treated like a joke (hence their reputation as the 'Laundering department'). The main character is now discovering this and he will attempt to make changes to prevent money from getting easily obtained and misused by other departments, especially the Knights order.
While it seems like the MC just wants to work and improve efficiency in his department, this will connect to the larger scenario of the kingdom undergoing a Magical crisis as the plot will reveal later.
The story and characters were just not it for me though. :/