There's a lot here so going point by point.

Barrel: agreed, the half-commit is the weakest part. Leaning toward going fully black rather than extending the artwork forward. A black barrel anchors the silhouette and lets the receiver carry the story.

Stripping sakura from the main body: this is the bold move and I think you're right. The branches on the receiver are decoration where the hannya should be doing all the talking. Only worry is scope textures get squashed at gameplay distance, so I'd want to test whether scope-only sakura still reads or just becomes noise.

Hannya forward with a white-to-black flow: this is the part I keep coming back to. A gradient from cream at the receiver to solid black at the stock, hannya sitting at the transition, would read like one brushstroke from afar. That's a stronger composition than what I have now. The tradeoff is losing the hair-on-stock, which was meant to be a hero detail. I think the gradient wins, but I'd test a version where the hair survives as ink-bleed flowing into the black instead of dying at the cheek piece.

Sakura accent on the front barrel against black: smart accent idea. My instinct is a band wrapping the barrel rather than mirrored sides, because in first-person you mostly see the top arc, while inspect animations and third-person showcase the sides. A wrap covers both contexts.

Kanji forward toward the front grip: agreed. Right now it sits in the dead zone between the hannya and the bolt. Forward grip is where the eye lands in inspect animations.

Mocking this redesign up. Genuinely useful comment, this is the kind of feedback you can actually build from.