Questions about this piece
What do you wear with a denim blazer?
Treat it as the jacket, not as denim. Keep other denim away from it, or at least in a clearly different wash, and let what is underneath stay quiet: a white tee, a black dress, pants in cream or camel. A denim blazer is what turns a plain outfit into a put-together one, so it earns its keep over simple pieces rather than busy ones. This one hangs open at the front, so whatever is underneath shows straight down the middle.
How should a blazer fit in the shoulders?
The shoulder seam should land right at the edge of your shoulder bone, not hanging past it and not digging in behind it. That seam is the one thing a tailor can barely move, so it decides your size; sleeve length and body width are far easier to adjust or simply live with. With this one there is no button and no lapel to pull across your chest, so the shoulder line is doing nearly all the work of how it hangs on you.
Do the ruched sleeves stay gathered?
They do. The gathering is built into the sleeve permanently rather than held by elastic or a tie, so it does not relax across a day of wear or need pushing back into place once the jacket is on. That keeps the forearm looking soft and shortened without any fussing, which is most of why a piece this clean still reads relaxed. Dry clean only, one denim color, sizes XS through L.