captain stag is well known brand in japan, at least in Oita , it has various range product, like camping equipment (tent, sleeping bag, stove etc ) and bicycle (including accessories).
I've bought captain stag folding bike bag.it is cheap and heavy and not ergonomic (at least compare to doppelganger folding bike bag), well the price speaks it self.
your bike may be some entry level daily bike, made in china-japan branded bicycle. many people use it here, some part might have adjustable issues ( front brake) but is good enough . was it coming with front basket and rear rack?