-さ

[mella]

どうぜつまらない将棋さ
Reading しおんの王, I found this sentence. I can grasp the meaning, but I don't understand this ending -さ

[Retsubty]

Are you sure it's Douze? Sa is an ending particle, similar to YO, kind of assertive telling somebody what something is.

[Hyperworm]

Would have thought it's どうせ.

Tried to find an online explanation for sentence-final さ, but I kept finding the mid-sentence kind of さ (which I feel is slightly different), and the explanations I did find about sentence-final さ didn't really hit the mark.

To me it sounds relaxed and casual. And in this case, a little dismissive (or that may just be the どうせ).

[Ongakuka]

Yeah, 'sa' is not assertive like particles such as 'yo' 'ze' etc. but it is designed to leave an impression on the listener, and in this respect it has emphasis, which may be what Retsubty-san meant. However, 'sa' is almost always has a laid back/casual/cool flavour to it, as Hyperworm-san said.