Regeneration

A Namekian trait that allows any Namek to replace limbs lost in battle. We first see this ability during the 23rd Tenka'ichi Budo￣kai 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 regenerate 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 has been defeated. During the Freeza saga Nail has his arm torn off by Freeza but regenerates it, much to the surprise of Freeza.

Later on, during the fight with Imperfect Cell, Piccolo has his arm drained by Cell leaving an emaciated brown stick. But Piccolo distracts Cell long enough to regenerate his arm back. Later still, in the Buu Saga, Piccolo demonstrates that he can regenerate from any wound so long as his head is intact.

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.

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.

Sai Sei may or may not be a basic part of all Namekians, since it may take some physical and mental training before Namek's can use this ability. 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 drain on the power level of the Namek.

Non-manga usage
This is also seen in DBZ Movie 4, utilized by Lord Slug. After transforming into a Giji form of Super Saiyan, Goku damages Lord Slug's arm. Lord Slug shocks Goku by tearing it off regenerating a new one. Similarly, in the same movie, Piccolo rips off his own ears to avoid hearing 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 the original Saban/Ocean Group English dub of DBZ, Tenshinhan made the claim after losing his left arm to an attack by Nappa that his arm would grow back. This was part of their attempts to sanitize the series; Tenshinhan, as well as 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 "Shiyo￣ken" below), he never said in the manga or anime (or future English translations thereof) that he could regrow lost limbs.

Character meaning
再 (Sai) - Again / twice / re-
生 (Sei) - Life / living / birth


Kanji / Kana：再生
Romaji：Sai sei
Translated：Rebirth
English anime：Regeneration
English manga：—
English Videogame(s)：—
Creator：Namek race
Other Users：Piccolo / Nail / Cell / Lord Slug