anime-analyst:

The one thing that bothers me about episode 13 is that child Hiro knows what marriage and love are while his older self has no idea.

You might say, “Oh, his memory was wiped, so of course he wouldn’t know!” That can’t be the cause, though. All of Hiro’s early memories of the Garden were totally erased, which is proven by the fact that he not only forgot about Zero Two, but also about his promise with Mitsuru. His fellow parasites, on the other hand, retained all their memories, which we see clearly due to the fact that Mitsuru still remembers the promise he made with Hiro; his memory hasn’t been touched. Yet even with their memories untouched, Hiro’s fellow parasites–their older versions, that is–have no idea what love and marriage are. If Hiro’s brainwashing did not cause him to forget what love and marriage are, then what did?

So that raises the question: why does child Hiro understand what love and marriage are in the first place? Since there seem to be no real life examples to go by, I assume that he learned about these types of relationships through books, which we know the parasites-to-be have, since they are shown to have a library. 

If so, then most if not all the parasites-to-be would know the definition of love and marriage, just like child Hiro does. Do all the parasites undergo a sort of selective mind-wipe that erases anything pertaining to love before they are sent out to a plantation and become parasites? Unlikely, for if that’s the case, it would be much simpler to just never allow them access to books containing romance.

It’s possible that Hiro was just given this knowledge by the writers so that they could point and say, “Wanna know why Zero Two is so knowledgeable about these things, while the other parasites can’t comprehend it? Well, it was actually Hiro who taught her all about it! Plot Twist!!!” Still, not only is that line of reasoning full of holes that I’m hoping someone on script writing duty noticed, but it also fails to explain where Hiro got that knowledge in the first place and why he no longer has it in the future.

Trigger and A1, you’ve got some explaining to do.