What is this kanji in Kaguya-sama's anime? In the anime Kaguya-sama wa Kokurasetai, Season 2, Episode 2, when Kaguya gives a fan for the Shirogane's birthday it shows that she wrote a kanji that, according the subtitles, is "Unyielding Diligence In One's Studies". 







I'd like to ask for some help if someone can copy paste this kanji here and if the meaning is correct. I tried to write it, but, as it's in Japanese calligraphy, I couldn't make it.
The kanji on the fan that was given by Kaguya is 磨穿鉄硯【ませんてっけん】.

According to weblio, the translation is correct:


  showing unyielding diligence in one's studies; wearing a hole through one's metal inkstone from constant studying


This is actually a yojijukugo or "four-character idiom" that is easier to search compared to identifying the characters in Japanese calligraphy directly.