Spell Battery

You have learned to withstand intense pain while still maintaining concentration on your magic, so much so that you can even apply these skills to spells intended to harm you.

Once per long rest, you may use your reaction when hit by a spell to store a copy of that spell within your mind. You may use a spell slot of the appropriate level to cast that spell a single time, as if it was a spell you already had prepared.

If you do not use the spell by the next long rest, you may spend double the usual amount of time and gold to copy that spell into your spellbook, contact your patron or god regarding your learning of the spell, or record the spell in another manner. Otherwise, forget the spell.