I'd edit my post if I were you, if you are going to use shadow manipulation and powers based upon that idea, I'd know the science behind a shadow. Directly, I won't bother to explain it, but I can tell you that Seru doesn't have a shadow because its body isn't in a state that shadow's require to be formed. If it did have a shadow you'd also have to take into consideration teh fact that Seru is above the ground and then apply merging into such a broken shadow from that.
I'll also tell you that in your post you stated that you can't take damage as a shadow, but that's impossible because absorbing yourself into a shadow makes you a physical direction of where light can't form properly; thus meaning erasure of the shadow before you get out of it, or inserting light into such a space via multiple means...could damage you.