Can you upgrade weapons in Dai?

Could you please clarify for me if it's possible to upgrade weapons in the game Dai? I've been exploring the game's features and haven't quite figured it out yet. Is there a specific method or technique to accomplish this? Also, if upgrading weapons is indeed an option, what are the benefits or advantages of doing so? It would be great to get a detailed explanation or some pointers on how to proceed with this aspect of the game. Thank you in advance for your assistance.