doshigatai 度し難い

In Japanese, doshigatai 度し難い means "irredeemable," "beyond salvation." However, the literal meaning of the word a bit more complicated. And given that this is a catchphrase in the manga and anime Made in Abyss, I supposed it deserves a thorough explanation.

Manga: Maid in Abyss, メイドインアビス (Chaper 15, 不動卿)

Meaning

Basically, doshigatai 度し難い is composed of three words: do 度, the auxiliary verb suru する in its ren'youkei 連用形 form, shi し, and the auxiliary adjective ~gatai ～がたい, which means "hard to do."

• do suru
  度する
  To persuade someone to understand.^{[度する（どする）の意味 - dictionary.goo.ne.jp, 2019-01-11]}
  To make them see the truth, the logic, to make them see the light.
  To redeem. To save. (from saido 済度, "salvation," Buddhist term.)
  • Not to be confused with:
  • dou suru
    どうする
    What do [I] do?
• do shi-gatai
  度し難い
  Hard to persuade-and-make-understand.
  Even if you tried to persuade someone, you don't think they'd understand.^{[度し難い（どしがたい）の意味 - dictionary.goo.ne.jp, 2019-01-11]}
  They're irredeemable. Beyond salvation.

By the way, this word isn't really as common in real life as it is in the manga.