Eren's father injects him with the Titan serum years before he first uses it. So how is it that he remembers how to activate it?

  • 4
    In ep. 15 Eren is asking himself the same question. So I think we'll find out later or you can check manga for spoilers.
    – Qiu
    Commented Jul 26, 2013 at 6:51
  • this needs to be updated with the latest info on time travel and stuff
    – user32029
    Commented Jan 8, 2021 at 23:03

5 Answers 5


I don't know how far the anime is yet, so I'll put it into a spoiler.

The shift between human is triggered by any injury that causes blood loss. The first shift is triggered when Eren gets eaten by one of the titans and hurts his arm. To trigger the next one, he bites himself to protect Mikasa and Armin. Apparently, also the will to accomplish something is needed to become a titan (kill the titans, save his friends)

  • So the first time he transforms it's basically by accident.
    – uncle brad
    Commented Jul 26, 2013 at 20:40
  • @unclebrad: Yep.
    – looper
    Commented Jul 26, 2013 at 20:43
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    Is that to say that Erin had never cut himself accidentily or otherwise before in his entire life? That seems a little unlikely to be honest. No kid goes through childhood without scraped knees or clumsy cuts from sharp objects. Commented Aug 15, 2013 at 15:23
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    @RobertEnglish He was hurt before for sure, but there was never a real reason to transform. As written, it seems like he needs the will to accomplish something.
    – looper
    Commented Aug 15, 2013 at 15:48
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    This still leaves room for chiildhood bullies(and the will to beat them), or the countless times he could have been injured (it's noted he's the most motivated of all the recruits) during his training as a soldier. Commented Aug 16, 2013 at 7:10

Rober English when eren has to turn into a titan he has to inflict damage on himself and have a clear goal so i'm guessing that when eren was a child he never had a goal like block the cannon or kill the titans

  • 4
    Your answer issent wrong but his power also activates with smaller goals. For example episode 19 at the 11th minute his goal is : Pick up the spoon. Gets schocked by the spoon. hand goes full titan mode
    – Dimitri mx
    Commented Jan 10, 2014 at 14:11

Its triggered by any injury that causes blood loss like Eren biting his finger but Eren must focus on a certain goal in order to trigger his titan form like for example kill all titans or it can be protecting Mikasa and Armin

  • I think your misunderstanding the question. It's asking how does Eren know/remember how to activate his Titan powers, not how to activate it. Commented Aug 16, 2014 at 3:11

He remembers how because when they explained how he turned into a titan it showed a flashback and his dad said "let these memories cloud your mind".

  • I have removed your "biggest question", but you can always ask your own in a new post, instead of in an answer.
    – JNat
    Commented Nov 19, 2014 at 12:49

I would imagine in order to transform the first time that you would have to be in very clear danager and would subconsciesly desire the change. He didn't have any concept that he could and something like getting cut on a tree would certainly not be dangerous enough to warrent the subconsciese into activating.

I would wager though that once he changed the first time and figure out he could do it it bacame much easier because he knew he could. It would be like discovering a secret talent that you had (wiggling your ears or something). You technically could always do it but without strong reason (someone telling you to try) you would never knew you could. Once you discovered you could, it would be much easier to access. (sorry if that's a bad example, not a lot of parallels to turning into a titan :p )

Another idea (though less likely imo) is that age has something to do with it. Maybe you have to mature to a certain point before it's possible. It just happened that he was finally of age/ ability at that point to turn and, with the obvious situation of being eaten, could at that point turn.

  • 1
    This is more of a comment than an answer. Most importantly it's lacking sources for the claims made.
    – mivilar
    Commented Sep 29, 2015 at 19:50

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