Headcanons about zanpakto in which I believe, part I
If shinigami lived a long live and his zanpakto developed his own personality and interest for the world, zanpakto spirit may become a human soul after their death.
Zanpakto have their own language, with writing system which is very hard to understand, because this language is meant for face-to-face conversation, so it depends not only from words and intonation, but also from reiatsu, gestures, and who and where is speaking.
Zanpakto can understand all natural languages and many artificial (if they are good enough). It is their innate ability, but initially they can understand only the mother language of their shinigami. Young zanpakto need to concentrate and perform work with reiatsu to understand new languages.
It works only for conversation, to read texts zanpakto need to learn language as usual humans (shinigami, quincy etc). But it is more easy for zanpakto because of their good memory.
Zanpakto have two main reiatsu nodes. One just below the collarbones, and other in the lower abdomen. When zanpakto is bound with shinigami, it looks like a rope of energy between the upper reiatsu node of zanpakto and Hakusuitosaketsu of shinigami (basically also the upper reiatsu node, but for human souls it works slightly differently). Shinigami can broke his bound with zanpakto by special rituals with secret kido.
Broken connection makes shinigami a lot of weaker, whereas zanpakto begin to die due to exhaustion, because zanpakto need shinigami soul to restore their reiatsu and be able to concentrate it from the outside.
Name is an important part of zanpakto. They have not only names which their shinigami use, but also their own names on their language. Their names contain important things about them and are developing with zanpakto. If zanpakto changes their master, they can (and usually do) change their name to be more accurate for new shinigami.
