Solider construct I is a very common enemy in the great sky island or other sky island as well, they can also be found in shrine sometimes. They will drop solider construct horns and one Zonai charge.
Solider construct horns can be used as an item to fuse on arrows, since it has a low fuse attack power on any weapon.
Zonai charges can be used to replenish your Zonai battery for 1 segment, if your energy is full, it will have yellow energy up to 8 wells.