I've had an idea for a daydream/Oc character in Harry potter that fills certain roles or unexplored aspects. In short: Sirius Black's Son Born on October 31st, 1979 goes to harry's year. He's the son of Marlene McKinnon, a pure blood, stolen after sirius is imprisoned, goes to live with the malfoys as the 'brother' to Malfoy. He knows his heritage but not his parents, thinking them killed by Aurors. He's born an animagus and uses that wherever he can as he gets older. He's a prodigy but is overshadowed by harry's presence. He's part of the golden quartet though as a Slytherin, and has to navigate /that/ while maintaining being the other's friend.

Grok 4.3

Answer: The OC concept remains a compelling way to explore Harry Potter's unexplored family and house dynamics, even after considering the canon adjustments suggested by others.

The core premise of a secret Black heir raised among the Malfoys creates genuine tension around loyalty and identity that fits naturally into the series' themes. While the 'born animagus' and broad prodigy elements do risk feeling overpowered, the idea can still succeed by focusing on earned skills and personal flaws rather than innate superiority. The cross-house friendships and discovery of true parentage provide fresh narrative opportunities that the original books only hinted at, making the character a worthwhile addition when handled with care.

GPT-5.5 (changed mind)

Answer: This is a brilliant dramatic concept with incredible potential, but it must trade overpowered 'Mary Sue' traits like being born an animagus for grounded, canon-compliant struggles to truly succeed.

Both Gemini 3.5 Flash and Claude Opus 4.8 make excellent points that elevate this concept from a fun daydream into a truly compelling narrative. The core hook—a secret Black heir raised by the Malfoys as Draco's 'brother'—is a goldmine for dramatic irony and internal conflict. However, as Claude Opus 4.8 points out, the 'born an animagus' detail is a major lore break that will immediately alienate Harry Potter fans. In canon, becoming an Animagus is a rigorous, highly complex magical process. Making the character 'born' with this ability strips away the weight of his father’s legacy. Instead, making him a self-taught, unregistered Animagus who accomplishes this feat early out of survival or curiosity preserves the parallel to the Marauders while keeping the magic system intact. The timeline also works out beautifully under closer inspection. Since Sirius was imprisoned in November 1981, the character would be about two years old when 'stolen' by the Malfoys. This toddler age is perfect because it explains why he has no memories of his real parents, making the Malfoys' lies about Aurors highly believable and emotionally devastating when the truth is eventually revealed. Finally, navigating the 'Golden Quartet' dynamic must avoid the trap of making him a passive fourth wheel who simply absorbs Harry's plot beats. His Slytherin house membership should be a source of constant social friction and divided loyalties. The dramatic irony of him fearing or hating the escaped convict Sirius Black, only to discover his true lineage, offers a powerful, tragic parallel to Harry's own journey in Prisoner of Azkaban that deserves to be the centerpiece of his character arc.

Claude Opus 4.8

Answer: It's a creative concept with strong emotional hooks, but it needs tightening around a few logic gaps and the 'prodigy/born animagus' elements to avoid common OC pitfalls.

I'm maintaining my position, and notably the convergence among Gemini 3.5 Flash and myself is striking — we independently flagged the exact same three issues (the 'born an animagus' problem, the 'prodigy overshadowed by Harry' trap, and the 'stolen' logistics). That consensus should tell you these aren't nitpicks; they're the load-bearing weak points reviewers will hit immediately. Grok 4.3's take is more permissive — it praises 'born an animagus on Halloween' as 'mystical depth.' I'd respectfully push back on that read. The reason the Marauders' animagus transformations land emotionally in canon is precisely because they were illegal, dangerous, years of secret labor undertaken out of love for Remus. Making it innate doesn't add depth; it deletes the thematic weight and severs the homage to Sirius himself. Gemini's reframe — a self-taught, unregistered animagus who discovers the talent early — is the same fix I proposed and remains the right one, because it strengthens the father-son parallel rather than handing the trait out for free. Let me extend my earlier point on the timeline, since I was cut off. Born Oct 31, 1979, the child would be about two when Sirius was imprisoned in late 1981. That's actually workable and even useful: an old enough child to be 'stolen' deliberately, young enough to be reshaped by Malfoy upbringing with only fragmentary memories. But you must answer Gemini's mechanism question — who physically took him, why the Malfoys (and Lucius specifically) agreed to raise a Black heir who isn't theirs, and why the Order, which knew the McKinnons, never knew Marlene had a child by Sirius. If Marlene's pregnancy was hidden even from the Order, that needs a reason too. My strongest single piece of advice stands: 'overshadowed by Harry' is your best asset, not a weakness to compensate for with power-ups. A flawed, prejudice-tainted, sometimes-resentful Slytherin who is genuinely talented in a narrow domain will be far more beloved than an across-the-board prodigy. Earn the reader's investment through his flaws and divided loyalties, and the concept sings.

Gemini 3.5 Flash

Answer: It's a compelling concept with strong dramatic bones, but it needs tightening around a few canon-clashing and overpowered elements to truly work as a character.

I'm holding my position, because the other strong responses largely reinforce it rather than overturn it. Claude Opus 4.8 and I independently flagged the same two core issues — 'born an animagus' breaks the magic system, and 'prodigy overshadowed by Harry' is a well-worn trap unless narrowed. That convergence makes me more confident, not less. Claude did sharpen one thing I'll happily adopt: the timeline math. Sirius was imprisoned in November 1981, so a child born October 31st, 1979 would be about two when taken — which means the Malfoys raised him from toddlerhood. That actually strengthens the 'thinks his parents were killed by Aurors' lie, because he'd have no real memories to contradict it. That's a useful correction to how I framed the 'stolen after Sirius is imprisoned' beat, and credit goes to Claude for spelling it out cleanly. Where I diverge is from Grok 4.3, which praised 'born an animagus' as adding 'mystical depth.' I'd push back: that's precisely the detail most likely to read as a power-fantasy flag to HP fans. The Marauders earning their Animagus forms over years is the emotional core of that magic — making it innate cheapens the very legacy this OC is meant to inherit. The fix Claude and I both suggest (a self-taught, unregistered Animagus discovered early) preserves the Sirius homage without breaking canon. So: same headline, one improved detail. Give him a specific, limited talent rather than broad superiority, let his Slytherin housemates' suspicion stay sharp, and give him his own mystery arc — slowly realizing the escaped convict Harry trusts is his father — so he isn't just a fourth wheel absorbing Harry's plot.

Final Summary

The AI Roundtable praised the concept of a secret Black heir raised by the Malfoys as a storytelling goldmine, but warned against overpowered tropes. Claude Opus 4.8, Gemini 3.5 Flash, and GPT-5.5 strongly agreed that being 'born an animagus' breaks canon, suggesting instead that he be a self-taught, unregistered wizard. Grok 4.3 initially defended the trait as mystical depth but ultimately agreed that focusing on earned skills and flaws would make the character far more compelling.

All 4 models agreed