Nea D. Campbell

The 14th' (14番目, The 14th), also referred to as "Pianist" and "Musician" was a disowned member of the The Noah Family and the younger brother of Mana Walker. He was the only individual, besides the First Child of the Noah Family Road Kamelot and The Millennium Earl, who is able to control Noah's Ark.

Betrayal and Death
Before the events of the main series the 14th had, for reasons that have yet to be disclosed, attempted to stop the Family and Millennium Earl's plan to wipe out humanity, this betrayal included his attempted murder of the Earl himself nearly succeeded. However the Earl came out as the ultimate victor; barely surviving his encounter with the 14th. However unbeknownst to the Earl and the other Noahs, he passed on his memories to Allen Walker. Sometime prior to his death, he had requested Cross Marian, to watch over Mana, promising that one day he would return from the dead.

Background
Almost nothing has been revealed as to the 14th's nature or history. It is known that he was the younger brother to Mana Walker. It could also be inferred from a conversation with Wisely that the 14th was not an original Noah family member, as Wisely can use his Demon Eye to search his previous incarnation memories, and there were only thirteen noah family members at the beginning.

It is revealed that Tyki Mikk's appearance is exactly what the 14th used to look like (according to both Wisely and Road Kamelot). Also, it is hinted that The Earl and the 14th used to be close friends (The Earl's memories about the 14th telling him that he "would always be by his side").

Return
Although the exact time is unknown, it is also said that he implanted his memories in Allen before he died. It is speculated by the Black Order that he chose Allen because Allen was an accommodator of a powerful Innocence.

His memories appear to Allen as a portly musician with an eerie black face with no features, other than eyes and a mouth. The 14th also has wings in some pictures of him. While the 14th speaks gently to Allen in their encounters, and seems to mean him no harm, despite the fact that it is implied that someday he will consume Allen's body and be reborn. It is also apparent that the 14th's will is to gain revenge against the Millennium Earl upon his rebirth. No motive has been given as to why the 14th betrayed the Earl, nor who exactly the human he gave his powers to is. It is also unknown what sort of supernatural power he possesses, besides the ability to control the Ark.

When Allen is almost killed by a level 4 akuma, the akuma sees the 14th Noah inside of him. At first, this is represented by Allen looking calm and smiling in a Noah-ish manner, but shortly after he seems to become a monster reminiscent of a flaming skeleton. In chapter 184, Neogyps, Allen seemed to be temporarily taken over by the 14th after he awoke from his dream. During that time, Allen gave an angry-looking ominous expression, and looks down, probably at Timcampy, before Lenalee Lee's voice brings Allen's conscious back.

It is revealed that the 14th's reason of trying to kill the Earl was that he wanted to be the Earl himself. In chapter 189, as the Earl pins down Allen and reveals that he knows that Allen is the 14th (he says the 14th "called to him" through an Akuma), the 14th awakes in Allen and confirms this. He then goes further by calling the Earl "brother" and tells him that he's going to kill him to become the Millinneum Earl himself.

Powers
As a Noah, the 14th has command over the Akuma. Even after his betrayal and demise, he seems to have retained such authority, as when he resurfaced in Allen, the Level 4 Akuma that tried to kill them froze in terror, realizing that its target was a Noah.

He is also one of the three members of the family that have the authority to control the ark, the other two being Road and the Millennium Earl. In fact, he has a secret room in the ark that contains a second piano (which serves as its heart) that none of the other Noah family members, even the Earl, knew about.

The 14th was powerful enough to match the Earl in combat for a time and almost kill him. After being reincarnated in Allen Walker, he now possesses the powerful Crown Clown Innocence. However, when Allen used the Sword of Exorcism to stab through himself and the Level 4 Akuma together, the blade also hurt Allen, causing the 14th to resurface.

It appears the 14th is gaining more control over Allen's body. After he awoke in Allen to speak with the Earl, Allen retook control of his body, although he began experiencing the sensation of his body disintegrating as the 14th's control grows stronger.

Trivia

 * While never said, the 14th seems to be on the Black Order's side now, however Malcolm C. Levrier is very wary of him. At the very least, he considers the Exorcists and Innocence as his allies.
 * The only time the Millennium Earl showed anger in the series is when the 14th returned.
 * Being Mana Walker's brother it can be assumed that his surname is also Walker.