In D&D 3.5, you can become an aflicted Lycanthrope if a natural lycanthrope of the same size category bites you and you fail the fortitude save. I wonder, though, how does one become a natural lycanthrope? I assume (may have read it somewhere, not sure) that the children of lycanthropes are born as natural lycanthropes. But that does not answer the full question: Where do natural lycanthropes come from? Is there a way for a full-grown person to become a natural lycanthrope, through curses or rituals or eldritch deals like in original werewolf folklore? While I don't necesarily need to know the origin of the first Lycanthrope, this would certainly help. My question would basically be: How would one become a lycanthrope without influence from other Lycanthropes.
Natural lycanthropes are usually born not made
The Monster Manual on Lycanthropes says
Sometimes a lycanthrope begins life as a normal humanoid or giant who subsequently contracts lycanthropy after being wounded by a lycanthrope. Such a creature is called an afflicted lycanthrope. Other lycanthropes are born as lycanthropes, and are known as natural lycanthropes. (MM 170)
Emphasis mine, but, of course, individual campaigns may vary.
Alternatively or in addition, a generous DM may allow a character to gain the template natural lycanthrope by undergoing a variant of the Ritual of Vitality (Savage Species 150).
Finally, the prestige class silverstar (Faiths and Pantheons 201-2) at level 6 gains the (presumably natural) ability Selûnite lycanthrope which says that
Upon reaching 6th level, silverstars who contract any form of lycanthropy are treated as natural lycanthropes. (202)
Whether a silverstar can pass on to its offspring this treated-as-natural lycanthropy goes unmentioned by the text. (The DM must make minor adjustments to the prestige class silverstar for compatibility with Dungeons and Dragons 3.5 anyway, so ask when he does.)
You can become a natural lycanthrope with a specific type of Wish.
This is explained on Page 150 of Savage Species.
A spellcaster casts wish and transforms the character. Ritual Time: 1 action, as the spell. Ritual Cost: The ritualist must spend 5,000 XP (the spell’s XP component). The ritualist charges the subject a number of gold pieces equal to caster level × 90, plus an additional 25,000 gp (to compensate for the experience point loss). Ritual Caster Level: 17th, as the spell.
You can become a natural lycanthrope through role-playing.
Bear with me here...
Perhaps you grew up into adulthood, without your parents ever revealing to you their/your true nature. Since you became an NPC under your DM's control, you have no memory of your changes throughout your life. Somehow, either by coming of age, the authorities arresting you, or your parents telling you - you have become aware of your natural condition and are indeed a lycanthrope.
XX + XY = XX or XY
Daddy werewolf and mommy werewolf had a baby werewolf. Some lycanthropes are simply born that way. (Credit: HeyICanChan)