Improve the loop you can see, then return with a clear next question
Anime Box Farm says that upgraded characters earn more money and that earnings continue while you are offline. The useful first move is to inspect the upgrade and character information available in your game session, then choose the next box or upgrade from what is actually shown.
There is no public cost table, money-per-second chart, or universal best-upgrade list for this game in the current source set. That means a good guide explains the progression loop and the limits of the available data rather than presenting made-up numbers.