Japanese book cover
帙 centers on a protective wrapping for books: a traditional Japanese book cover or slipcase that encloses and preserves the volume.
帙 combines 巾 (cloth) with 失, which likely contributes a phonetic element. The character originally referred to a cloth wrapper or case for books.
The left side 巾 is cloth, and the right side 失 looks like a person losing something. Picture a cloth cover that prevents you from losing your book: 帙 is a book cover.
For チツ, imagine a book cover that fits so tightly it makes a 'chitsu' sound when you slide the book in: chitsu -> チツ.