A cheerful red-haired Exorcist of mixed race, who aims to become a Bookman and is working along the Black Order just to be close to the events that must be seen. To help him, he developed an incredible memory: he is able to memorize every single aspect of something he saw, but he commented (in chapter 101) that he could identify "the key" (the key which Tyki Mikk gave) faster if he were to use both his eyes when sieving out the real "key" from the fake. He is 18 years old, and normally uses his left eye while the right eye is covered by an eye-patch. His anti-Akuma weapon is a size-shifting hammer, which he calls Oozuchi Kozuchi (大槌小槌, lit. "big hammer small hammer") or Nyoibo. It can grow (満, man) or extend (伸, shin). The weight increases with its size, but since Lavi is the conformer, the weight does not effect him; However, it does to everyone else. His hammer can also summon several "judgments" with kanji possibly representing the classical elements that can be used individually or combined. However, between some of the seals are question marks. This probably means that Lavi has some seals that he has yet to learn from his Innocence. His techniques so far, are:
- Hi Ban: Gouka Kaijin (劫火灰燼火判, lit. Fire Seal: Conflagration of Ash): using the fire seal to create a torrent of flames with the form of a snake;
- Ten Ban: Raitei Kaiten (雷霆回天天判, lit. Heaven Seal: Thundering Lightning Whirling in the Skies): using the heaven seal to liberate an immense lightning;
- Moku Ban: Tenchi Bankai (天地盤回木判, lit. Wood Seal: Roots Entwining Heaven and Earth): using the wood seal to control objects in nature;
- Konbo Ban: Gouraiten (コンボ判剛雷天, lit. Combo Seal: Strong Thunder of the Heavens): using both fire and heaven seals to create a huge snake of fire and iron. Also making a shield-like flame wall.
It was shown when Bookman told Lavi to use the wood seal to clear the clouds (Three Akuma were hiding behind the clouds). Lavi stated that he forgot he could use it to affect nature directly, and as he remembered it the question mark turned into a kanji that he used right away. If seen more carefully the kanji for the wood seal can be seen throughout the manga whenever Lavi summons his seals long before the use of the actual seal itself (e.g. during the use of the heaven seal). At the moment just before its first use the seal can be seen just behind Lavi's head and had never transformed from a question mark in the first place.
The marks of water and earth also appear among his seals. He likes to call Bookman "Panda" due to the thick black circles around his eyes; a converted Akuma "Chomesuke"; and Arystar Krory"Kuro-chan" in the anime and "Kro-chan" in the manga. He is the only character other than General Tiedoll to call Kanda by his given name (that name being Yuu, also translated as Yū or Yuu), and apparently speaks to him outside of missions, a fact that was shown when he called Allen "beansprout" (moyashi), saying that if Kanda could call him that, Lavi could as well, as he is the same age as Kanda. He has a habit of teasing Allen, and deems himself as his big brother. A recurring gag in the series is Lavi's fondness for beautiful older women, whenever he sees a woman his type (Example: Eliade) he'll yell out "Strike!" with hearts in his eye.
There are many different translations of his name, such as Ravi, Rabi, Labi. But it is found in the D.gray-man Omake from episode 61 that the correct spelling is Lavi.