Acquiring a living weapon is no small task. You must find a sorcerer-blacksmith, and you must either befriend or betray him, that he might coax what dangerous forces be into wood, bone, leather, and iron that might armor your spirit. He must know who you are - you, your family, your lineage - and what spirits stalk your path. He must lure them into the motherly forge to be reborn in iron. He must feed them with a blood temper.
Then, you will have a weapon with no limits.
You must feed your living weapon with blood once a month, on every significant holiday, and on its birthday, or else it will grow angry and curse you. It will not remind you, it expects that you remember.
The more blood fed, the more powerful the weapon becomes.
The better blood fed, the more powerful it becomes. The best blood comes from dragons and other high predators. Livestock and other tasty bloods provide high sustenance but require high volume.
Some bloods are blasphemous. Those born of social taboos or of aberrations are most blasphemous. The weapon will wretch and scream to be offered such things.
Blood to power works on orders of magnitude, on logarithmic scales.
5 Blood Offerings = +0 Weapon
25 Blood Offerings = +1 Weapon
125 Blood Offerings = +2 Weapon
600 Blood Offerings = +3 Weapon
3,000 Blood Offerings = +4 Weapon
15,000 Blood Offerings = +5 Weapon
And so on. There is no limit.
In general, the Blood Offerings of a creature is equal to its Hit Dice.
Small livestock will be 0 HD, providing sustenance but little gain.
Large livestock will be 1 HD, providing one Blood Offering.
High Predators, such as lions, rocs, or basilisks provide triple their HD in Offerings.
Dragons provide ten times their HD in Offerings.
Normally, only one Offering may be made per day. A Living Weapon needs time to gorge.
Only you, or someone closely related to you by blood may gain the benefits of the Living Weapon. Your father could use it, or maybe someone in your clan. Your twin could use it as good as you. In fact, a twin is indistinguishably the same person to a Living Weapon as its original wielder.
Every Living Weapon gets one effect from the below list for each +1 it has.