The anime talks about the characters leveling up, as if they somehow know that they aren't real. If you or I gained more skilled, we'd say we became more advanced in X skill, or were more skillful that we were previously. Or is this something that is in the manga's backstory that isn't fully explained in the anime?
3For reference, in episode 12, the Japanese script says 「ここは空気も薄い、過酷な環境での実戦、結構レベルアップしたんじゃないか？」, mentioning about "level up". (Just providing an instance of it, not attempting to answer)– Aki Tanaka ♦Jul 29, 2017 at 2:08
Well in the dub for anime some one has to come up with the words for the script to the best of their ability.So it's just their choice in words.
If I read the manga, you're saying that they wouldn't talk about leveling up? Aug 27, 2017 at 21:05
I never saw the manga.And i don't remember lvling up.It could be their in the manga but they are not required to use the exact words as in the manga. Anime scripts are usually longer than the conversations in manga. Aug 27, 2017 at 21:08
I will vote up, but can't accept the answer. I'll wait until I get an answer from someone who knows the manga inside and out. Aug 28, 2017 at 0:13
More than likely it's a slightly inaccurate translation of a word or phrase that means to "improve" or "become more skillful".