Regeneration is an ability that allows its user to replace limbs lost in battle and recover from similar severe damage.
Most Namekians are able to use Regeneration (再生 Sai Sei, literally, Rebirth). We first see this ability during the 23rd Tenka'ichi Budôkai after Goku redirects Piccolo's own homing Tsuihidan back at Piccolo and damages Piccolo's arm. Piccolo then proceeds to tear the injured arm off, to the horror of the spectators, and regenerates a new one.
In the Vegeta Saga we see this again after Piccolo loses another arm from Raditz's twin beams which he regenerates after Raditz is defeated. During the fight with Imperfect Cell, Piccolo has his arm drained by Cell leaving an emaciated brown stick. But Piccolo manages to distract Cell long enough to regenerate his arm back. Later on, when Semi-Perfect Cell blasts a hole through Piccolo and throws him in the ocean, he can still recover thanks to regeneration ability. Later still, in the Buu Saga, Piccolo demonstrates that he can regenerate from any wound so long as his head is intact.
- Note: The head is where the "regenerative nucleus" (a.e. the regenerative organ) is located.
Cell acquired the ability by being created in part by Piccolo's cells, absorbing that part of his Namekian makeup. On several occasions Cell regenerates from extremely severe wounds, including one which left no part of his body except for the regenerative organ intact (this was not only thanks to this ability, as it a combination of Sai Sei and Frieza's ability to survive horrifically severe wounds and still live, even function).
Lord Slug uses Sai Sei in DBZ Movie 4. After transforming into a Giji form of super saiyan, Goku damages Lord Slug's arm. He then shocks Goku by tearing it off and regenerating a new one. Similarly, in the same movie, Piccolo rips off his own ears to avoid hearing Son Gohan's whistling tune (unbearable to Namekians' sensitive ears) but later uses Sai Sei to instantly grow his ears back, to everyone's amusement.
In it unknown if Sai Sei is a basic part of all Namekians, since it may take some physical and mental training before Nameks can use it consciously. It also appears to be quite an exhausting procedure, every time after it is performed the user is breathing extremely heavily from the effort and strain, and requires absolute concentration of mind and body. It has been pointed out that regrowing limbs causes a severe temporary drain on the power level of the Namek.
Meta Cooler has a similar ability, though it is more mechanical in nature. It should be noted that Meta Cooler (the first encounter) is not the "real" Cooler (he is revealed to be one of many mechanical copies of the original Cooler; these "Meta Cooler" bodies where created by the Big Gete Star), the "real" Meta Cooler is the still living disembodied-head of Cooler that had merged with the Big Gete Star, with Cooler's head becoming one with its core. Like Frieza, Cooler has the ability to survive virtually any wound (like being vivisected in half or decapitation) and function (as seen with both Frieza and Cooler).
Baby's ability to liquefy may give him a form limited regenerative abilities, that are likely bio-mechanical in nature.
Also, Bio Broly has a similar ability to regeneration, as demonstrated when Krillin makes a direct hit to Broly's head, but it regenerates and reattaches the head.
Majin Buu seemingly has a similar ability, allowing him to regenerate lost appendages, holes in his body, recover from being blown to pieces, or even being blasted to vapor. In his case though, his entire body is in an unstable form and each singular piece of him, even as a fine dust, is able to reform back to his original shape. Buu's regeneration is not Namekian in nature since he was able to regenerate wounds long before he absorbed Piccolo.
In the English dub of Dragon Ball Z, Tien made the claim after losing his left arm to an attack by Nappa that his arm would grow back. This was another attempt to sanitize the series: Tenshinhan, just like any other human, has no ability to naturally regrow lost limbs. Although he does have the ability to grow extra limbs temporarily for combat use (see Shiyōken technique), he never said in the manga or anime (or future English translations thereof) that he could regrow lost limbs (Note: Had he not been killed in the fight with Nappa, Tien could have used a Senzu Bean to restore his left arm).
Users (Sai Sei)
- Most Namekians (Sai Sai)
- Piccolo Daimao
- Kami (may have allowed him it to survive the use of the Evil Containment Wave technique)
- Dende (being Namekian Dende should be able to)
- Cell (Taken from Piccolo)
- Lord Slug
- Meta Cooler (Nano-regeneration - Any injury Metal Cooler might suffer is instantly detected and repaired, and whatever flaws in his design that allowed the injury are corrected.)
- Majin Buu
- Super Buu
- Kid Buu
- Rage Shenron
- Omega Shenron (With the power of the five-star Dragon Ball)
- 再 (Sai) - Again / twice / re-
- 生 (Sei) - Life / living / birth