• 筆箱ふでばこ — pencil case
• 毛筆もうひつ — writing brush
• 筆記ひっき — writing / note-taking
• 筆者ひっしゃ — author
• 筆跡ひっせき — handwriting

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The kanji 筆 combines the bamboo radical ⺮ and the component 聿, which refers to brush-making tools. It originally described a writing brush made from bamboo and animal hair.

By extension, 筆 came to represent writing itself, handwriting, and the role of an author.

新あたらしい筆ふでで 書かくのは 気持きもちがいいです。
Writing with a new brush feels great.

筆者ひっしゃの意見いけんに 賛成さんせいです。
I agree with the author's opinion.