Midori, Age 12, is a yonkoma styled comic strip in every volume of the Midori Days manga. They are non-sequitur joke panels often having little to do with the actual plot, and are typically just quick gag cartoon strips. They come on the pages prior to the advertisements or messages from the author, are typically situated next to a caricature of Kazurou Inoue that sits above a short explanation of who Mr. Inoue is, and may come after the "The Days Before Midori Days" bonus chapters Or the "Planetary Girl, Ultra Marin" Bonus manga. Although volume six contains seven bonus yonkoma called "Extra Midori Days", the ones that are "Midori, Age 12" are the ones whom are headed by this name.
The volume shows Midori stating her age and that she likes dogs. She then nuzzles a dog who proceeds to chomp her and put her in his mouth. She then states she doesn't like dogs very much right now.
Seiji and Midori appear to have just stepped out of the bath, and state that nothing is better than coffee flavored milk after a bath. They notice Rin who also got out of the bath, who chugs a tequila bottle and notes nothing is better than tequila after a bath. Seiji and Midori note Rin likely won't live long with this lifestyle.
Seiji and Midori are in bed, enjoying the sound of the rain. They then drift to sleep. The captions note they were 'once again' late for school.
Seiji shows Midori his guitar. He mentions he was a rocker when he was younger, and we see Seiji beating up a gang member with a guitar while yelling "ROCK!!!". Midori asks if he thinks that is what a rocker is, and Seiji responds somewhat annoyed that he knows. A rocker has to take advantage of the width of the guitar when whacking with it. Midori then just asks him to play her a song.
Midori asks Seiji if he likes hot girls. Seiji then goes on to list several traits other than physical looks that he likes about girls. Rin tricks him into saying he likes big boobs, and he yells at her for it. He also yells at Midori for then drinking a whole carton of milk.
Mr. Inoue apparently sent the characters in his comic a VHS with the first episode of the Midori Days anime on it. They pop it in to watch, and it turns out to just be The Ring. They call up Mr. Inoue, who appears to be laughing at the joke he played on them. Seiji states he wants to punch him and Midori doesn't argue.
Midori is reading an article on palm reading and asks Seiji to give her his palms to read. Seiji points out she is one of his hands. She sits there confused, then begins trying to figure out where Seiji's palm would be if she's his right hand. Seiji asks if the two can just eat already.
Seiji apparently gave Midori the diary from the final chapter that she's been keeping the entire series. She reads it over and is embarrassed at how open she was with her feelings. She then writes in her own diary that nothing's changed about how she felt, Seiji notes she's still exactly the same as before.
- It isn't stated if these are supposed to be canon or not. Considering Mr. Inoue, the manga's author, sent a VHS tape to his characters in volume 6, this is likely not. This would also mean that Volume 8's is also non-canon, or a possible alternate ending.
- Volume 8's does not bookend the book like the other volumes. Instead, Volume 8 ends with an epilogue explaining what happened to Takako and Kota which comes after Midori, Age 12.
- Volume 6, as stated in the opening, contains 7 more yonkoma in total for eight in a single volume, although 7 of them are canon and the Midori, Age 16 at the end may or may not be.
- Rin is the only other character than Midori or Seiji to appear in them.