Soul Units are 7 special artifacts that contains Norse's important components. It can also be used on other LBX, a few of them being Hiro's Azure Persues & Ban's Lance Elysion. The effects are entirely unknown but it grants LBX a boost in an certain catergory of ability in a state of emergencies.
The units also seems to have a life of their own like when Ban & Hiro tried to fight some Sea Serpent LBXs in Historical Musuem with their newly repaired Persues & Elysion after the destruction of the Icarus duo but failed, two of the units acted up & flung into the almost-destroyed Persues & Elysion; repairing them & remodeling them.
It also rumored that the Soul Units can connect one player's senses with their LBX. This may been the origin to TRAL's LS Fields since they have gotten their hands on a few of them already.
Finnaly, the Soul Units' existance have been hinted & written in the following sentence:
"When the 4 Eastern Beasts & 3 of the knights of Round Tables returned to Avalon, the gate to Rebirth shall open,"
- The Soul Units are based on 3 of the Knights of the Round Table & 4 mythology creatures from the chinese constellations.