I have just finished the anime, and althugh given that the show did a really good job at tying up loose ends with the plot, I still do not get Roswaal L Mathers' purpose within the plot. According to my memory, he was/did the following:
- Head of the mansion and the Mathers Domain
- Helped with the fight between Subaru et al. and the majuu packs
- Sponsored Emilia for the election
...But then he wasn't seen within the show afterwards (for the latter section, at least).
Did his character play a bigger role that I overlooked? (Or potentially in a later release of the manga that has not been anime-tized?)