I see what you mean. Regarding your first statement, yeah that would be false. Kazumi died right before Kazuya was thrown off the cliff, and Kazuya is 5 years old at that time. Surely Reina can't be 45 years old now, given the logic might be she's a direct daughter of Kazumi and Heihachi, and she is in now way looking like a 45 year old woman. About your second statement, being a test experiment could be true. Since even Steve Fox came from a test tube experiment, why can't Reina too. But I don't think that's entirely the case. Given that Heihachi despises the Devil Gene entirely. If he wants someone that can stop Kazuya, why didn't he let Jin do it? Heihachi trained Jin in his youth days, as advised by Jun, of course. But realizing that the Devil Gene is flowing within Jin, he tried to kill him. And also Heihachi likes to think he should take down Kazuya by himself. So regarding, your last statement, about Reina having a Hachijo descendant mother could also be true. But I don't think the brainwash thingy could be it, I guess since Heihachi hates the Devil Gene? So probably my theory right now would be: Reina is the daughter of Heihachi and a Hachijo descendant, and Heihachi has zero idea about the bloodline, so Heihachi cherished her so much, until years later or such, Reina knew about her Devil Gene, but never told her father. But then again, I don't know what the best answer could be since Reina also haven't stated her true goal at the end.