Offical Canon Laws
1. By ancient law two Shinigami cannot hold the same zanpakutō,
they must fight for the honor of bearing the spirit, with the spirit going to the winner.
2. It is forbidden for a Shinigami to acquire hollow powers.
3. It is against the law for a Shinigami to use forbidden Kido.
4. It is against the law for a Shinigami to give their spiritual power to humans.
5. It is against the law for any citizen of Soul Society to create weapons of a dangerous nature not sanctioned by the feudal government, to do so is treason.
6. It is against the law to commit terrorist action or attempt overthrow of the balance of Soul Society, to do so is treason.
7. It is against the law to commit murder.
8. It is against the law to attack a captain, to do so is treason.
Note: Breaking these laws might get your character kicked out of Seireitei. Stll, the Gotei 13 will only know if you've broken them if player characters that see another player character breaking one, and then telling them in a storyline post. Thus, a player can avoid being banished if they manage to keep it a secret.