[explanation]
OVERALL:
All in all, the way I play this 14th is based off of the very vague information we have so far on him, as well as the basic idea of How Noah Act, judging by the other Noah with more canon. Also, because of how he is using Lavi as a host instead of Allen, I also through in some of Lavi's personality. I realize that most of this is probably AU even without meaning to, but it's my interpretations of the canon and how everything works.
LAVI/WALKER & 14TH?:
Yes, yes, in canon, when the Musician fully awakens, they've said that his host (Allen) is going to be taken over, and basically disappear. Allen will become the 14th and they keep hinting nothing will be left of Allen at all once this happens.
However, the way this AU runs, my 14th was forced to take action and takeover far eariler than he meant to. Because hey, the plan was to at least have a position inside the Order before announcing himself, really. But when Walker decided to end both of them, the 14th had to pull him back from death, and this sort of melded them together in this AU. The 14th can't get rid of Walker and Walker can't get rid of the 14th, not without ripping their minds apart--which, could be done, but isn't pleasant at all, and would probably drive whomever was left partly insane.
This also gives more reason for the 14th to have quirks of canon!Lavi's personality. While, no, Walker and canon!Lavi are very different people, the base of them remains the same--what would be called "Junior" by most. The 14th has adopted this into himself without knowing (because hey, there isn't a canon!Lavi in his world to compare himself to, or another of himself to see how he's changed) and twisted it to be better suited for harrassing the Order--hence, the similarities to Bookman Junior's forty-ninth persona: "Lavi".
BEING A NOAH:
Because of the melding described earlier and the fact the 14th is sort of a secondhand Noah (Mana's brother was the proper Noah, but he put HIS memories into the host and the Noah Memory sort of came along for the ride) I play my 14th as a bit weaker Noah than would be if he had simply awakened like Skinn or Wisely. This doesn't mean he's an easy kill, but there's a reason he uses the Innocence Hammer along with his powers, even when it scars up his hands. He heals just a bit slower than a normal Noah (Rhode notwithstanding, considering her DreamWorld form) and his powers don't stretch as far as they once might have. Speaking of which--
NOAH POWERS:
This is where I pretty much just go "aw hell, well it's AU, if I'm wrong... well it's already AU". My 14th has power over sound. As long as there's something to vibrate (air, water, etc) he can use that vibration as a weapon. This of course leading to his main weakness--if a Tyki just rejects everything around him, there's nothing he can use for his powers. At that point, he'll probably rely on Walker's Innocence to get him out of that mess.
He can cut, whip, and stab things with sound--sort of like a wind attack, only it's riding on the burst of soundwaves rather than the wind itself. He also can affect things with different forms of sound, as long as there's sound to use. Mainly this involves him making the sound--by humming or whistling usually--but he can also use other people's sounds for himself. So basically if you could paralyze him completely (gagging wouldn't work) so he couldn't even tap his foot against the ground, you had better be able to muffle your own sounds or make them soft enough that they're useless as a weapon (breathing is not enough sound, but a loud footstep might be enough to smack someone).
OTHER NOAH POWERS:
He also has a few secondary powers related to music--that aren't all that useful in battle unless you're really crafty. One is that on a complicated and strong melody, he can play images like a movie. The images that appear are related to a)the song itself, b)who is playing the song, and c)his own mood at the time. So it's not like he can just play random movies or something on a song, but say, if there's a song based on a memory of an event, and the person playing it remembers the event or knows about it, the 14th could possibly play that event out in an aurora-sort of lightshow.
His other secondary power is to hear people's Music. Which basically amounts to the song of their soul. Unless he is well acquainted with someone, he won't be able to tell more than basically what sort of person they are. It takes more interaction with the person to notice the little changes that signify moods and behaviors. At it's least helpful, he could use it to find people if he can recall the Song he's listening for. He also hears anyone's Music who is nearby him, all the time, he can't turn it off without turning off his Noah--so he's very good at ignoring the Music as well.
In the DR, this talent is mainly rendered useless because many people are the same person and therefor have very similar Songs. That being true, it will take him longer than usual to be able to tell one person's Song from another. (This means I'm not going to use it to godmod character interactions, and also probably won't mention much about your character's songs unless you give me permission. At most I try to stay very vague about what he hears from characters and any mistakes can be dealt with through "well I got your Song confused with someone else's Song".)
GOALS/PLANS:
To kill the Earl and take his place? ... You'll find those out when the rest of us do. Until then, keeping it vague and pro-human, anti-Earl. (Also, be very, very afraid whenever any of the 14ths decide to plan together. |D )
STALKER? WTF?:
Okay, the way I interpret the Noah is that they're generally an unconsciously creepy group. That's just how they are and they really don't mean it intentionally (not all the time anyway). And the 14th is not an exception to this rule. While he may not have been a creepy, possessive bastard before his Noah awakened, he is now. The possessive part, is really my own twist, and I highly doubt is truely canon, however in this AU the 14th's possessiveness was sort of spread out onto all 'his' Exorcists, and so while it might have prodding its head up now and again in his home world, it wasn't at the scale it is in the DR.
To explain why he's so intensely possessive in the DR, first I have to explain that the 14th is a firm believer in 'originals'--he doesn't want copies of his things, he wants the original item. So while he might be automatically brotherly with a Mana, he knows they're not his Mana, and therefore no strong possessive feelings. And the real reason he's so intensely possessive in the DR, is because suddenly 'his' things/people are drastically limited. There's his room, his hat, his clothes, and his worldmate(s). Hence, he suddenly is very possessive of all these things. In the DR, while a lot of the people remind him of 'his' people, until he actually gets to know them and such, he won't be so possessive of them. He still considers all Exorcists 'his', but not as much as the ones from his world.
Why is he a bastard? Because he's fucking insane. His worldview is completely and utterly screwed up. Try dying and being reborn only as a set of memories in a host who you're unintentionally driving mad just by your existence. He doesn't think his possessive tendencies are a big deal, nor does he think much of randomly maiming or killing people (who aren't 'his'). He's still a Noah (although slightly more insane than a normal Noah), it's just that he's on the Exorcist's side instead of the Earl's side. He's still a bad person--just a bad person who's on humanity's side.
WHY SO AWKWARD?:
For the most part the 14th has three ways of being: fond-teasing, mean/angry-teasing, and creepy-teasing (leave it up to you to decide which one he's using, since they all sort of turn out the same way). However, in my headcanon, the 14th and Mana were already busy with the Earl and Akuma at an early age (teens, like Allen) and with his new host, the 14th was, again, forced to push away normal childhood interaction for the War.
This means that the 14th doesn't really understand, completely, the way humans are supposed to relate to each other. He's only dated in the most vague of terms, and never seriously (most likely not dated at all and just had a few one-night-stands now and again). And basically he doesn't quite know how to be normal friends with a person, or relate to them on a personal level. When someone doesn't agree with him, he's more apt to push it off playfully, than actually acknowledge that they have a point. This makes him stubborn and closed minded to things at times.
It's not so much him trying to be awkward, but that he will dive headfirst into things without realizing that the end result is something he has no idea how to deal with--or alternately, he'll avoid interactions he doesn't like by teasing and generally being obnoxious and childish about it. This usually makes people upset with him or make them think he's even more insane than he acts. He's just not so good with people, when they're not Mana, or other Noah (who usually try to kill him, but whatever).
--
TO AROUND UP:
... Yes.. so basically he's a creepy, possessive bastard, who enjoys humans and doesn't like his Noah family.