The Grail Reliquae is placed in the centre of the front rank, just like a standard bearer or musician. If the unit reforms, the Reliquae is always moved to the front rank again, just like a standard bearer or musician.
The Grail Reliquae has a 5+ armour save. In close combat, this save is increased to 4+.
The Grail Reliquae counts as both a standard bearer and musician. While there are rank & file Battle Pilgrims remaining in the unit, each wound caused against the Reliquae will result in one regular rank & file model being removed. Only once all the Battle Pilgrims are removed does the Reliquae itself start taking wounds.
In addition, the presence of the Grail Reliquae means that the entire unit will be affected by The Blessing of the Lady, if the Bretonnian army prayed at the start of the game. This follows all the normal rules for the Blessing of the Lady.