When all Vessel Fragments have been collected the name of the Inventory item changes to Soul Vessel
Fragment of a white vessel made to contain soul.
Collect more to form a full vessel, allowing you to carry more soul.
Soul Vessel description
A complete vessel, imbued with the power to contain soul.
Vessel Fragments are parts of Soul Vessels. 3 Vessel Fragments complete a Soul Vessel and increases the Knight's maximum SOUL by 33%. When the main soul meter has empty space, any SOUL stored in the Vessels will automatically fill up the main meter after a short delay.
It's important to note that, while each Soul Vessel grants 33% more SOUL to use, the amount of SOUL it takes to fill each Vessel is actually 66%. Because of this, if a player is in a long fight and is constantly gaining SOUL to use for Spells or Focus, it is better to use the main meter as soon as possible, as there is a delay between running out of SOUL in the main meter and having it be refilled by the Soul Vessels.
With a total of 9 Vessel Fragments in the game, the Knight can acquire 3 Soul Vessels, doubling the maximum amount of SOUL they can carry.
There is a total of 9 Vessel Fragments to be found in the game:
While the fountain in the Ancient Basin will always ask "Drop all Geo into the fountain?", only a total of 30003000 will be added. Any extra will not be subtracted.
There are unused sprites found in the game files which suggest that a Soul Vessel originally consisted of only two Vessel Fragments, showing two halves which needed to be collected to acquire a full Soul Vessel. This was changed to three fragments for the final release.