How are made up words for anime/manga formed (reading and kanji)?

Question

EDIT: Eiríkr Útlendi has answered my question mostly in regards to readings. What remains is how kanji are chosen for their meanings and why certain words are selected over others e.g. 実 versus 果実. Also there are exceptions to the rule e.g. 天竜人{てんりゅうびと}. How do those factor in?

I've been watching the Anime "One Piece". There are quite a few compound words that obviously seem made up for the universe, and when I look them up the constituent kanji either don't follow the readings they would as original words [example 1] or they use a listed reading that doesn't occur in any words I can find in my dictionaries [again example 1] (I use ejje and Jisho). Otherwise, there are words that use readings that appear more archaic or irregular to me [example 2 and 4]. Then there are words that use the kanji and readings of the original word (in example 3, "emperor"), but only part of it (in this example, only one of the kanji of 皇帝 and thus only the reading from one kanji). Maybe my vocabulary is too poor and I'm making mistakes because of that, but here are the examples:

Example 1: 三{さん}刀{とう}流{りゅう} Translated as "three sword style" - This makes sense, except why is とう and not かたな used?
Example 2: 海{かい}楼{ろう}石{せき} Translated as "Sea Watchtower Stone" - 2nd makes sense, but I don't understand why かい is used for the 1st and not うみ and せき (I can't find any words with this reading) instead of いし for the 3rd.
Example 3: 四{よん}皇{こう} Translated as "4 emperors" - Why just こう and not よんこうてい
Example 4: 七{しち}武{ぶ}海{かい} Translated as "7 Warlords of the Sea" - Here かい again. Also why use the irregular reading しち?

Example 5: ゴムゴムの実 Translated as "Rubber Rubber Fruit" - Why not 果物 or 果実?

Is there a logic to these? Are they just made up to sound cool? If so, how will I know when reading a new manga what these made up words mean? Someone can definitely tell me that I'm overthinking this, haha.

Thanks for your input.

Answer 1

Made-up words are generally based on the existing Japanese naming convention. I generally recommend that you familiarize yourself with a lot of Japanese existing compounds before wondering about this problem at this level. Especially distinguishing on- and kun- readings is critical. Please read this section carefully.

三刀流

If you already know a word 二刀流, this should look natural. さんかたなりゅう makes almost no sense to me. And See Eiríkr Útlendi's answer. It's a simple on-on-on compound.

海楼石

The author just followed the standard naming convention of rocks. See: 岩石の一覧. Basically all rocks are technically named as ～石【せき】 or ～岩【がん】. かいろう is a simple on-on compound, which looks far more natural than うみろう.

四皇

四皇帝 makes sense, but both 皇 and 帝 already mean "emperor", so you don't have to keep both of them. Similar things happen all the time. For example, 法律 ("law") is a compound made of two kanji with the same meaning (法 = "law", 律 = "law"). Only 法 is used when it forms other compounds: 民法, 六法, 諸法. Another example is 道路 ("road"), which is made of 道 ("road") and 路 ("road"). There are many compounds which only use 道 (国道, 車道, 歩道, ...). 四皇帝 is fine but seems less interesting as a made-up word. And there are many two-kanji compounds where only 皇 is used to mean "emperor/imperial": 上皇, 皇位, 皇籍

七武海

It's just a on-on-on compound. ななぶかい is not impossible but would sound a bit strange.

ゴムゴムの実

Read Sino-Japanese vocabulary first. There are many related questions on this site (for example this, this). Basically 果実 sounds more formal/technical than 実. In this case I feel 果実 wouldn't go very well with ゴムゴム(の), which is another made-up word that sounds nothing technical/formal.

天竜人

てんりゅうじん (yes, simple on-on-on compound) would perfectly make sense in modern Japanese. As you probably know, じん the default suffix when we plainly refer to イギリス人, 日本人, 宇宙人, etc. But ～びと was used a lot in the old days to refer to "people of/in ～". So using びと adds the old/historical/traditional nuance to it. For example, 外つ国人 （とつくにびと） is a word preferred in samurai dramas to refer to foreigners.

Answer 2

Before diving into manga word-formation patterns, it is important to understand how kanji readings happen. Kanji have two readings: the kun'yomi (literally "meaning reading"), which is based on ancient native-Japanese vocabulary, and the on'yomi (literally "sound reading"), which is based on the borrowed Middle Chinese terms. The on'yomi is often used in kanji compounds, such as the とう in 三刀{さんとう} or the かい and せき in 海楼石{かいろうせき}. Also, there is nothing irregular in the しち reading for 七.

I'll leave the word-formation topic for other posters.

Answer 3

To answer your ゴムゴムの実{み} question. They could used 果物 or 果実; it's not wrong. And likewise, ～の実 is not wrong as well. 木の実, 草の実 are common. I can't say why one was chosen over another, outside of maybe because it rolls off the tongue better (less syllables).

To answer the 天竜人{てんりゅうびと} question. it still follows the same base of "using readings familiar to Japanese speakers". (I'm skipping the 天龍{てんりゅう} part, since that follows the on-yomi rule Eiríkr Útlendi has mentioned.) Although the reading itself is not that common, there exists words that use 「～ひと／びと」 reading in compound kanji, such as 天下人{てんかびと} and 稀人{まれびと} (note that I won't go into detail about why these are pronounced like they are; that's a whole different topic). So to a native speaker, they will see the reading and think "Ah, that makes sense." Note though, 天龍人{てんりゅうじん}　still is most likely the first choice of native speakers, and without ルビ would likely default to this reading. Which brings me to the answer below.

Real answer: Fictional words are formed any way the author wishes.

The author can designate any reading to kanji they wish. This is quite common in manga, games and literature today. So technically, if I were the author, I can say 天龍人{ドラゴナイト},　天龍人{ドラケン}, 天龍人{りゅう} or whatever other reading I can think up. Sometimes completely irrelevant readings are used, to give the word a double meaning, so with your case I could say 天龍人{てき} to show they are the enemy.

So really, the answer to most of your questions is something only the author would know. If the reading is unusual, there will almost always be ルビ to help you read it. Otherwise, on-yomni is always the safest bet.