Short bonus comics or extra material added to a collected volume, usually lighter in tone than the main story. Read from the closing, as a 9.
9A 9 by its term: humanitarian & sage, and therefore the closing.
Omake translates roughly as extra or bonus. In manga it refers to short strips and supplementary pages included in a tankobon that did not run in the magazine.
Typically four-panel gag strips, character sketches, author commentary about deadlines and assistants, behind-the-scenes notes on how a scene was drawn, or short scenes cut from the main story for space.
Tonally they are usually comedic even in otherwise grim series, which produces the common experience of finishing a devastating volume and immediately encountering the cast in a chibi-style joke about lunch.
Usually not, and rarely intended to be. Omake generally sit outside the story proper, though some authors use them to deliver genuine supplementary information about a setting.
For readers interested in how manga is actually made, author sidebars are one of the few consistently available windows into working conditions and process.
Every letter here carries a digit; together they make 18, which folds down to 9.
What the 9 brings is reckoning. The reference files it as a completion. Whatever else this entry is doing, it is doing it with the 9's sense of a cycle closing and something being released.
The vowels alone reduce to 3, the consonants to 6. Expression underneath, responsibility on the surface. The gap between them is where the subject is most interesting.
The 9 asks you to work out what survived the ending. The 9 sentimentalises. An ending is not automatically a meaning, and the reference tries not to pretend otherwise. The other entries that reduce to 9 are collected on The Closing.