This is the trademark ability of the Akimichi clan. When performed, the Akimichi grows in size, proportionately increasing their weight and strength and thus making their physical attacks more powerful. Such a significant change in size places a great burden on the user's body. As such, users typically are not seen maintaining the Multi-Size Technique for long periods of time, instead reverting back to their normal form after they've concluded their series of attacks. During the Fourth Shinobi World War, Chōza and Chōji Akimichi at one point seem to use the Multi-Size Technique for several hours.
There are two ways the Multi-Size has been depicted in the series. The first is where the user becomes extremely round, with most of the body's expansion being applied to their torso; because this is what happens to Chōchō Akimichi when she uses it, she dislikes performing it. The second is where the user simply becomes larger, bigger than their normal size but not so big as when they use the Super Multi-Size Technique. Chōji uses the first during Part I and the second during Part II and onwards, suggesting the user's age has something to do with it.
- During the Fourth Shinobi World War, use of the Multi-Size Technique is shown to produce extra markings under the user's eyes. Such markings are not present in earlier depictions.
- Rin no Sho, page 215
- Naruto chapter 337
- Naruto chapter 536
- Boruto episode 59
- Naruto chapter 537