Wait! Have we actually have had it confirmed that Aokiji and Akainu are real titles or just nicknames they changed to upon promotion…? Such as I had understood it Aokiji, "Blue Pheasant" was just something that was cool for an name to work under, sort of like how Edward Newgate prefers to use Whitebeard rather than his real name, and yet Whitebeard's not a title.
Such as I had understood it, "Blue Pheasant" was just an alias that Kuzan/Kazan begun using upon achieving the status of an Admiral, in the same way Edward Newgate uses "Whitebeard" or Shanks uses "Red-Hair" without it being his real name or a title, but simply a name to symbolise his power.
But yes, I know, just because Whitebeard isn't a title doesn't mean that Aokiji couldn't be a title either, because Whitebeard's a pirate and Aokiji's a marine, and there's quite another system of titles in each one of the two different fields.
However, I keep to my theory that Aokiji/Blue Pheasant is as much as a title as Shirohige/Whitebeard is.
And that Sengoku would be a weird name? Tss…
Some examples:
Don Krieg is simply a pll together of that title you keep hearing in mafia-movies and Krieg's simply German for war.
Smoker, Crocodile, Captain Kuro, and Kuma is soooo simple that I would feel embarrased if I would try to explain it. (When Smoker recently got promoted, he didn't change his name, and yes, I know that Smoker's in English and not Japanese as Sengoku)
...and then we got all that bunch of women with bird-names that nobody puts into question, all of them japanese.
Fullbody Ironfist, that's very weird name too, as Oda's actually explained the meaning of Fullbody.
Usopp isn't even a real name, it's just a play on words of Aesop (If you actually doesn't know who Aesop is, then you're free to check him up for yourselves) and the Japanese way of saying "I am a liar!", and yet nobody seems to wonder how that can possibly be his real name.
Therefore I would say that Blue Pheasant is probably a name to symbolise power, as Red-Hair or Whitebeard, but that Sengoku's probably his real name, and, it might sound a bit weird but, hey, so does almost everybody else! To conclude my theory, if now Sengoku is his real name, then "the Buddha" would might be the name he uses to symbolise power (As Bellamy "the Hyena").