Starlight Blade: Ceruleus

+3 Greatsword, 2d6 Slashing, reach, heavy
{w} Whilst wielding and attuned to this weapon, you may tether yourself to another caster of immense importance. As an action you may forgo taking an action yourself, and instead use the blade as a makeshift gate to allow your companion to cast as if they were in your space. This does not consume their turn, though does expend spell slots and materials as normal.
At last you have found it. Your guiding starlight. She will be with you, and you will