[Comparing a shard to materia might not be too far off, actually. Is there a life materia or maybe a creation one? If so, shards would probably be the most like them.]

If you want something to protect your sword permanently--and I would recommend that since it means so much to you--then I would look for someone to place actual protective spells or runes on it. Shard magic cannot be used constantly as it will drain energy just like any other skill will and then you will need to rest and recharge. You don't want to leave your sword unprotected during times when your shard energy is low.