As shown by Eps. 51 and 67, Subaru has still has major self-image issues with him thinking he’s such a loser for having been the only one to lose his cool and his insecure remarks to Julius lightly throwing a jab his way as someone self-confident wouldn’t have been phased by Julius’s remark. While I can see why somebody would think it was just a casual roasting between friends, I don’t think that was the case.
What backs up my read is that people who have unresolved trauma are more likely to lash out ’cause those with strong memories of past unpleasant situations may have disrupted/irregular emotional regulation if they were impacted by them enough, and that was definitely the case with Subaru’s inferiority complex centered around his dad. Even Naoko’s comments in the 1st Sanctuary trial put pressure on Subaru to become half as cool as his dad, who’s a freaking gigachad, so while that may have alleviated some of the crushing weight he felt being in his dad’s shadow, his feeling of being in Kenichi’s shadow didn’t go away entirely and wouldn’t from a talk like that for somebody with a trauma as complex as his centered around failing to live up to being his dad’s son and also how he was abandoned by those he’d developed surface-level relationships with just to act out in an effort to compensate for his not being as great as his father was.
Thus, given all Subaru has achieved up until this point, the previous Subaru still being stuck in a state of self-loathing necessitated amnesiac Subaru challenging that by saying that Natsuki Subaru is an amazing guy as he’d experienced all of the challenges and all the setbacks that the previous Subaru had gone through to know that he’s objectively achieved a lot even if he needed a lot of support to do so unlike in many of the anime and light novel isekai slop he’d most likely consumed before being summoned to the fantasy world.
This was an excellent use of dissociation in fiction with how amnesiac Subaru reading Subaru’s Books of the Dead and how the two Subaru’s interacting helped the other understand something about himself he hadn’t realized, which any serious take on dissociation needs to get across, and better yet, the two of them merged into one rather than one just absorbing the other, showing that Tappei does his research on the subject matter for his story, and I expect amnesiac Subaru to keep up the good fight in pushing against Subaru’s poor self-image in a corner of his mind in his long journey to achieving self-love. I believe Episode 82’s title being Subaru’s named episode was very appropriate. Once again, this episode demonstrated how much care Tappei put into his story in creating an enjoyable and layered narrative by using an amnesia plotline as an avenue for character development rather than simply as a plot device.