from what i see in the concept, this cyan blue metalic part that is in the upper part of his arm (between wrist and elbow) it seems like a glove without fingers that extends to the back of the elbow. This could function as the base to attach the weapons on, unless you like the idea of some metalic sculpture coming out from…
You could make it come out of the skin. Since this character looks like is an experiment from some scientist,and is enhanced with technology as well, you could make the weapon attatching to some form of metalic sculpture coming ouf of his skin(if those arms and legs could be justified as flesh) . This would also make it…