On the Principles of Transformation, maybe? Or perhaps I should approach it from the other end with Dagmar Ibsen's Theory and Practicality in Inter-Species Breeding? Ailis ran her finger along the spines of the books on her shelves, considering. Then she shrugged and pulled both down. More ideas wouldn't hurt at this stage.
She settled onto a cushion with her research material and a steaming cup of tea. I can see two direct paths using Beast Magic. There might be other ways with other Skills, but I must work with what I have. She opened Principles of Transformation and scanned the table of contents. Definitions, categories, recommendations... Ah, here, long-term effects. She skimmed the chapter until she found what she was looking for.
Beast Magic tends to favor either temporary changes or wholesale creation rather than permanent alteration. While this is preferable in most cases, it causes difficulties when attempting to modify livestock or other beings in a way that passes on to future generations. Beast Magic spells with a fixed or Concentration-based duration are not feasible for such projects, as such magic fades when the transfer of genetic information occurs.
"Hmm," Ailis mused. "But what if I do not care whether the trait breeds true?" She searched further, this time turning to the categorization chapter.
For those of more prurient interests, sexual compatibility transformations come in three main types. The first, superficial modifications, only alter the target's appearance or abilities without affecting deeper biological functions. These are sufficient for all but the most depraved or specialized uses.
The second category is reproductive modifications, which change the target's biology to allow impregnation by or insemination of a wider range of creatures. There are two further subdivisions of this category: a practitioner can change either the reproductive cells directly or the organs which make such cells. The former is difficult, requiring precision and care, but it produces effects far more quickly and can be done with temporary-duration spells so long as there is no need for enhanced traits to be passed on. The latter is still an advanced usage of Beast Magic, but one which does not require a Master in the field. However, it takes time for the new organs to produce modified sperm or eggs, and if the effect is to breed true, it requires permanent alteration of the subject's body.
Finally, there is the most drastic measure, embryonic transformation. Only true Masters of Beast Magic should dare attempt this, for even the slightest error can cause sterilization or death of the mother. Embryonic transformation involves encoding genetic information directly into a viable egg cell. When performed perfectly, this allows the practitioner to design the resulting child from the ground up. Needless to say, this must be done with permanent magic.
Ailis closed the book and drummed her fingers on the cover. "So it is possible, but will require a specialized spell and, in the safest iteration, take considerable time." She set Principles of Transformation aside and opened Inter-Species Breeding, turning to the section on centaurs.
Centaurs are one of the least-fertile races in the Realms, leading many scholars to speculate that they are a manufactured species. Centaurs are only fertile with creatures that share their non-humanoid body type. In the case of the standard Plains Centaur, this means other equine-based centaurs, horses, ponies, and donkeys. This holds true in both directions. The children of centaur/animal pairings are always centaurs of the same subrace as the parent. Some unscrupulous individuals have used this fact to breed the rarer subraces in captivity, but such is rarely successful in the long term as the centaurs almost always commit suicide when they realize what is happening.
In addition to having a narrow range of viable breeding partners, centaurs suffer from low fertility in general. Female centaurs only ever release eggs one at a time, and only during their estrus cycle, which occurs every three to six months depending on individual and subrace [data on Grey Centaurs is insufficient at this time owing to their resistance to capture or questioning]. Compared to the eggs of either of their related species, centaurian eggs have a thicker cell wall and are much more resistant to penetration by sperm cells. Centaurian sperm, meanwhile, are over-specialized to deal with this and tend to render equine eggs non-viable either due to rupturing or the introduction of multiple instances of male genetic material.
Some experiments have been performed in altering centaur genetics to lessen or eliminate these issues, with mixed results. Enhancing centaur-to-centaur fertility is fairly straightforward using Beast Magic spells similar to those used for other races and species. Researchers have also had success in breaking the heat cycle in some centaurian subraces, allowing them to follow a more frequent and less harsh fertility period similar to humans and other humanoids. However, cross-breeding efforts have met with limited success at best.
By far the most promising example of a centaur cross-breeding project was performed by the esteemed Archmage Steinar. In experiments lasting four decades, he created spells that altered four volunteer female centaurs' reproductive biology, which broadened their fertility to include the humanoid half of their biology. According to his records, each volunteer was successfully impregnated, but only the Plains Centaur bore her child to term; the other three miscarried early in the pregnancy. Each of the children was a centaur of their mother's subrace, implying that any centaur/non-centaur pairing will result in a centaur child even when magically induced. Archmage Steinar's notes indicate that he attempted a similar experiment with male humanoids but could not achieve positive results.
"So," Ailis mused, "it looks like there is one viable option before me: creating a spell that temporarily changes Aidan's sperm or testes into those of a centaur. Permanently altering him in that manner will not work if he intends to have children by Sunnild, and changing Brighid is likewise out as it would only extend her fertility to Moon Elves, which Aidan is not. We could always shapeshift him into an Elf, but that would be excessive and increase the risk of miscarriage."
Ailis finished her cup of tea and stood up. She returned the two books to her shelves, refilled her tea, and then pulled out a slate tablet and a narrow piece of chalk. "I think that I will go for whole-body transformation; partial polymorphs are always tricky to integrate with the rest of the body. Besides, Brighid should have the chance to experience having a centaur mate at least once in her life." Nodding to herself, she began to sketch. She had a couple of hours still before she was needed elsewhere.
Ailis
Early Afternoon
Ceallach Macht
"So, you decided where to put the Tabernacle?" Ailis asked Brighid. They were walking down the central avenue towards the outskirts.
Her daughter nodded. "Yes. There are a few potential sites, but Aidan and I want to divorce worship and rulership in the people's minds. There were only two locations that are more than a couple of minutes walking from Caer Macht and the Forum, yet still within the planned city walls. Of the two, I chose the one nearer the main gate."
Ailis nodded back and asked, "You wish to make it easier for visitors to find?"
"Exactly. From the description, the Dreaming Tabernacle will bring visitors from all over the Realms. Gerwyn tried to persuade me to place it further from the gate so that visitors would have to pass more shops and stalls, but I held firm. After all, there is no guarantee that pilgrims will receive the chance to visit the Dreamlands on their first attempt. I doubt that the Gods wish to be pestered by hundreds of petitioners at every hour of the day."
"It is good to hear such wisdom from you, daughter," Ailis told Brighid with a warm smile. "In truth, I doubt that the location will matter much in the long run, but I can tell you thought a great deal about this." She lapsed into silence for a moment, then said, "Aidan has been good for you. I... approve of your choice of mate."
Her daughter snorted and tossed her hair. "I appreciate that, but you know that I would be with him even if you did not approve, right?"
"Peace, little spark, peace. I am only trying to correct my past mistakes. When you brought him before me, smelling of each other and touching each other below the table—" it was Ailis's turn to snort as Brighid shot her a startled look "—yes, I knew what you were doing. Your arms were moving. I am not blind, daughter. When you brought him before me like that, I thought it an act of rebellion, a way for you to hurt me as I had hurt you. I know, now, that was stupid of me, but at the time, it seemed like you were using your relationship as a weapon against me."
Ailis shook her head and chuckled in wry amusement. "Of course, that was before the pair of you finished destroying all of my carefully-constructed pretensions. And it would be hypocritical of me to censure you for having a relationship with someone I am pursuing like a mare in heat."
"Now, now, Mother, if you were that desperate, you would be farther along than you are," Brighid teased her. "I love Aidan, but it turns out that women who throw themselves at him are his weakness. He talks a good game, but he is starved for affection. From what I have seen and heard, he loves deeply but never met a woman who was willing to return his affection in kind until me." She gave Ailis an appraising look. "I do not know as much about you, though, Mother. If you want, I can help you drive him wild?"
"Hah! Twenty-two years old, and she thinks she needs to tell her mother how to seduce a man." Ailis waggled her finger at her daughter. "How do you think you came about, hm? I was hardly the only one after your father's attentions, you know."
Brighid frowned. "Actually, no, I do not know. You have never said much about Father. All I know is that he was a wanderer and left the village when I was still very young."
Ailis blinked and thought back. Had she never? "Oh, Brighid, I am sorry. I never meant to hide him from you. I guess... I am a bit embarrassed. Your father—Magnus Farstrider was his name—was quite handsome, and he knew it. He probably mounted three-quarters of the unmated women in the village and more than a few of the rest. I was just the one with the highest status, and so the one whose home he slept in." She shook her head. "He never made any promises of fidelity to me, but every night when he came home to me, it fed my pride. And, so far as I know, I am the only one he got with child, though I have no idea if that was intentional or not."
"What was he like, aside from being a rakish scoundrel?"
"Oh, there was much more to Magnus than that. He was as strong and tireless as any other Adventurer, but he also had a razor-sharp mind. He had a gift for reading non-verbal cues and interpreting things left unsaid. He would have made an incredible politician. As for what he was like? I would not call him kind; there was a darkness, a sort of indifferent cruelty to him that, I confess, made him even more attractive to me at the time. He loved to fight, both sparring and real combat. If he was not busy with a woman, he was either at the training field or out hunting monsters."
"Like a male Ysbail?" Brighid sniggered.
"Hah! Yes, sort of. I suspect that only people with their rough-and-tumble approach to life become Adventurers. He was very, very good at it, though. He seduced every mare he set his eyes on, cleared our entire territory of dungeons, lairs, and wandering beasts, got me pregnant, then left."
"Wait, he left before I was born? Did he know you were carrying his child?"
"Yes to both questions. Like I said, Magnus was not a kind or compassionate man. He came, he conquered, and then he left when there was nothing more of interest to him. He stayed until I started to show. I think he wanted to make sure I was pregnant to leave a legacy of his passage." Ailis gave a rueful chuckle. "I know that does not paint a pleasing picture of either of your parents, but I want you to know that I never regretted you for an instant. I love you, Brighid; always have, always will."
"I love you too, Mother." Brighid stepped in front of Ailis, forcing her to stop, then swept her into a tight hug.
Ailis returned her daughter's hug and tried to contain the tears of joy that threatened to spill down her cheeks.
Zurai
Special thanks to Cenomy, Orange, and Somedude for their exceptional support on Patreon!