Ok, before I post, make sure to NOT lot that patron come out again, unless he's EXCESSIVELY WEAKER than he just was. By power scale, Prisma is excessive, and his presence is purposely meant to catalyst the plot into motion.

An energy blast capable of blowing up an entire tavern is far beyond what, for example, Jenso is capable of in his hero tale, and he's already at chapter 60+ at 1111+ posts. I'll try and rush the plot towards explaining your sword, or at least getting some backstory in on it, but your patron should not be able to go toe-to-toe with someone like Prisma for more than a couple of seconds in the future. From the tone, it seems like your patron is some obscene power boost that you already have full access to, rather than something that can grow in power over time.