realistic birth fanfic

A reader reincarnates in the world of Mushoku Tensei as Seraphim Greyrat, the first son of Paul and Zenith born instead of Rudeus. Using his meta knowledge to the fullest, he aims to become the strongest existence of that world, using both sword and magic. ###The Fanfic is dropped. Learning from the experience, I'm writing another Mushoku Tensei fanfic - Fate/Mushoku Tensei: Reincarnated with Servant's Potential (Mordred).### ... Warning: A SLOW PACE FANF-FIC WITH A LARGE FOCUS ON MAGIC STUDY AND WITH A HIGH LEVEL OF DETAIL. STARTS OFF SIMILAR TO CANON. Seraphim studies the magic system of the world and Battle Aura techniques in depth to understand them fully and gain the best possible advantages. He becomes overpowered without external cheats, a result of his hard work and brains. Note: How this fanfiction is different from others in that many Mushoku Tensei fanfics seem to often get the magic system of the world wrong. The abilities that the Protagonists develop often go against the magic system of the world, are illogical and ridiculous, and something like this in my opinion completely breaks immersion. For example, ridiculous new magic spells and OP sword moves that get invented by an infant MC despite the fact that they are completely devoid of logic and are just impossible without cheats. Here, my Protagonist faces various obstacles and problems during training, that he should, while also gaining insights and does what is realistically possible to take his training and fighting methods to another level. He also achieves things that seem nearly impossible or fantastical, but with good logic and reason behind them. -It is a harem story, but I aim for meaningful romance and deep relationships. It is a harem story. However, harem is not the major focus of the story at all. It only means that the MC will have more than one partner EVENTUALLY. -Because the Protagonist accomplishes A LOT during his early years, there might be no real romance or even harem content anyway for something like 100 chapters. There will be no child sex here as well. There might be some romancing and teasing, but just that, nothing sexual. How this story is different from the original is that it is not about an MC searching for a cure for his ED, being passive and pathetic pervert all throughout the story while screwing around and doing nothing most of the time, but is a man on a mission. Seraphim starts from a similar point as Rudeus, but his actions cause a slowly spreading butterfly effect as he's focused on the most optimal path and BENEFITS. In contrast to Rudeus's perversion, the MC can sometimes instead be amoral and do evil pragmatic things for the sake of his ambitions and loved ones, so people with fragile hearts be warned. He is not as disgusting, but it doesn't mean he's a goody-two-shoe white knight. ... SUMMARY: -MC is born instead of Rudeus with just his meta knowledge and high talent. Taking more after Zenith, he has blonde hair and blue eyes. He trains his mana from an extremely young age, masters Battle Aura and chantless healing magic | A genius of magic and the sword, a determined true main character pursuing supremacy and eternal life. -The story will have a deep dive into the magic system and how the MC interprets it (how I interpret what we know using logic). It might be boring for some people, but it can be very interesting for others (would be for me). -The story starts with the same layout, and has slowly spread out changes as the MC is focused on BENEFITS. -The world is the same as in the original, the only AU change is the MC's body, looks and name.