It's time for a little Japanese lesson, about Mr. Sakurai's nickname.
In Japanese culture, social status is a very important concept; so important that it's built into the grammar of the Japanese language. When speaking Japanese, you always have to be mindful of the status relationship that exists between you and the person you're speaking to, because the level of formality of your speech will depend on whether or not your interlocutor is of higher status, lower status, or equal status to you. There are a lot of different factors that determine what your status is in a given context. Status is a relative concept, it changes depending on the people around you. Basically, anyone older than you has higher status than you, and anyone your age has equal status, and anyone younger has lower status, but other factors come into play as well, including things like what your profession is or what year you are in school.
In Japan the concept of "in-group" (uchi) vs. "out-group" (soto) is also very important. Once again, uchi and soto are relative concepts. Your family is your most basic in-group, but if you work for a company, your company is also your in-group. Within your company, the employees with the same seniority status as yours are your in-group. If you're a student, anyone in your class is your in-group. Et cetera. It changes depending on the situation.
Anyhow, the Japanese language allows for many possible layers of politeness and formality. In general, if you are addressing someone who is of higher status than you are, or you are addressing someone who is not a member of your in-group, you need to use formal speech. On the other hand, if you are addressing someone of lower status than you are, or a member of your in-group, you can use more informal speech. The level of formality will depend on your relationship to the individual person, and the context. Formality can be expressed in a lot of ways, but verbs, verb forms, pronouns, and name suffixes play the largest role in determining how polite you sound.
Basically, in Japanese, referring to someone you're speaking to directly by the pronoun "you" is either very informal or intimate, or it's rude. If you're speaking to someone directly, you have to use the person's name.
So for example, let's say you're talking to a guy named Imai, and you want to ask him if he likes a big fat horn section. You can't say, "Do you like a big fat horn section?" You have to say, "Does Imai like a big fat horn section?"
Only, you can't just say "Imai," you have to say "Imai-san." That is, you have to add a name suffix. When you use someone's name when you're speaking to them directly, you always have to add a name suffix.
Which name suffix you use depends on your status relative to the person you're speaking to, and on the context. There are a lot of name suffixes, and they have many different uses, but the most common ones are "-san," "-chan," "-kun," "-sensei," and "-sama."
The most basic name suffix is "-san." It's like Mr. or Ms. in English. It's general and it's polite...and one huge advantage it has over English is that it's non--gendered! You can use "-san" for just about anyone, male or female, though "-san" is not generally used for children, or for people who merit the suffix "-sensei." You usually use "-san" for people who are higher status than you are, but "-san" is also used for people of equal status or perhaps even lower status than yourself, if they are not a member of your in-group. As always, it depends on the context. But you should probably call this Imai guy "Imai-san."
The suffix "-sensei" is used for teachers, but it's also used for doctors, or anyone who is very accomplished or eminent in his or her field. Since this Imai guy is a really famous, well-respected guitar player, you could also conceivably call him "Imai-sensei," if you wanted to draw attention to how much you respect his 1337 guitar skillz.
The suffix "-sama" is at least as polite as "-sensei," but more general. However, "-sama" usually only gets used in very specific contexts: if you work in a service industry and are addressing a customer or client, or if you are addressing a letter, or someone you don't know to whom you want to be very polite.
The suffixes "-chan" and "-kun" are informal. You usually only use them for people who are of equal or lower status than yourself. So when Mr. Sakurai goes out drinking with a starry-eyed Nishikawa Takanori, he calls him "Takanori-kun," but Takanori is calling Sakurai "Sakurai-san," for sure (if they are drinking buddies, calling him Sakurai-sama would definitely be overkill).
In general, "-kun" is used for boys and men and "-chan" is used for girls and women, but that's not a hard and fast rule. Girls or women who are seen as having some sort of "masculine" quality can sometimes be called "-kun," and in general, "-chan" is more informal and more endearing than "-kun," so sometimes it's used for men as well, when "-kun" just isn't snuggly enough. Also "-chan" is often used for all children, regardless of gender.
Calling someone by their name without a name suffix is called "yobi-sute," and it means you are very, very close to that person.
Which brings me to nicknames.
Perhaps it has something to do with the fact that Japanese is such a complicated language when it comes to politeness and forms of address, but Japanese people all have nicknames. I think they get sick of the formality. As I already intimated, in formal contexts in Japan, such as work, school, etc., people will almost invariably address each other by their surnames + san. Imai-san, Sakurai-san, Yagami-san, etc. If Cayce's last name is Pollard, Cayce would be called Pollard-san.
But! In informal contexts, that is, among your friends or your in-group, people call each other by their nicknames. Sometimes Japanese nicknames have nothing to do with a person's real name, and instead are somehow related to something about that person resembles, etc. For example, a friend of mine who was into Sweet Lolita fashion often got called "Pink-chan," because she was almost always dressed in pink. But most of the time, Japanese nicknames are shortened versions of a person's real name. And because Japanese nicknames are based on the rules of Japanese phonology, there's a right and a wrong way to make a nickname.
Which brings me to Mr. Sakurai, and his nickname.
Mr. Sakurai's correct and real nickname is "Acchan," but I notice that overseas fans have given him other nicknames, such as "Atsu" or "Sushi." Neither of these latter nicknames would actually be phonologically possible in Japanese.
"Sushi" is impossible because the name "Atsushi" is made of three morae: "a," "tsu," and "shi" (a mora is a Japanese syllable.) In Japanese phonology, morae are indivisible units. You can't break them in half. So you can't split the name Atsushi in half to get At-sushi and then just call him "Sushi."
"Atsu," on the other hand, would be possible except for the fact that even with nicknames, you still need to use a name suffix, usually "-chan" or "kun." But when the mora "tsu" is found in the middle of a word preceding a voiceless consonant (like the "k" in "kun" or the "ch" in "chan"), the "tsu" gets compressed into the voiceless consonant, to form a geminate, or doubled, voiceless consonant. In plain English, basically, "tsu" likes to stick to other voiceless consonants.
Therefore, "Atsu" + "kun" = "Akkun"
And "Atsu" + "chan" = "Acchan"
I'm also going to add that you can't use more than one name suffix at once. I already mentioned this in the comments section of another post, but since "Acchan" already contains the name suffix "-chan," you absolutely can't call him "Acchan-sama."
"Acchan" is really the most obvious way of forming a nickname for anyone who's name begins with the syllables "Atsu." Amusingly enough, it's been all over the Japanese news lately that idol Maeda Atsuko has "graduated" from AKB48. Her fans are upset and keep posting things on Twitter like, "Noo, Acchan graduated!" As you can see, it's not a very unique name. "Acchan" is such an obvious nickname, in fact, that it's possible if not likely that Sakurai has been called "Acchan" his whole life, starting when he was a small child.
As for Buck-Tick fangirls calling Mr. Sakurai "Acchan," it has some interesting implications. I know that some overseas fans have been curious as to whether the "Acchan" nickname is rude. It's true, using such a familiar nickname implies great closeness. Not even Sakurai's friends refer to him as "Acchan," with a few exceptions such as Mr. Yagami. They pretty much call him "Sakurai-san" if they're younger than he is and "Sakurai-kun" if they're older. So why are fangirls allowed to call him "Acchan"? Well partly, it's because a lot of the Japanese fans have been following Buck-Tick for 25 years now. They've been fans of the band almost since the band were the awkward kids we saw in this post. When they started calling Mr. Sakurai "Acchan," he wasn't a 46-year-old with the gravitas of a vampire, he was just a 19-year-old kid with white satin pants and hair sticking straight up. But also, a lot of fangirls clearly feel that calling their favorite band members by endearing nicknames brings them closer to the band...though if they ever met the band members in person, they would surely use "-san" or possibly "-sama."
Even so, a lot of Japanese Buck-Tick fans feel that at this point, the "Acchan" nickname is a little outdated. That at this point, Mr. Sakurai is old enough and accomplished enough that he really deserves a little more formal respect on a regular basis. Those fans never call him "Acchan," they always call him "Sakurai-san."
So how does Cayce feel about it, then?
Frankly, I think it's a stupid nickname.
I mean really, does this guy look like an "Acchan" to you?
But, here on Blog-Tick, we revel in stupidity, so there you have it.