I feel like any Reimu origin story wouldnt be complete without a tragedy and Yukari somehow getting involved. Like spiderman i suppose
Well, the fact of the matter is that Reimu's family is completely unaccounted for, while we know where Marisa's is. Every other human we either know who their parents are, or can at least assume they're possibly on the other side of the barrier.
My personal theory/headcanon is Miyadeguchi Mizuchi killed the previous shrine maiden, which is why reimu's afraid of vengeful spirits and furthermore she actually possessed Reimu to do it, the memory of which was suppressed by Yukari employing a suima.
*fssss...*...I'll practice writing talismans in my room.....We're having omelette rice for dinner.
You like it, right?Hehe*zyum*...Just like an ordinary mother and child.To think I'd see you playing parent.You're one to talk.