このうガニはヒトの(human)顔(face)あります！
ヘイケガニのなまえはかたかなですから、このガニもおもしろいです！
I chose to select ヘイケガニ as my Katakana Analysis focus word for a very specific reason. Whilst neither claiming a vast knowledge in theoretical linguistics nor Japanese (far from it in fact), even within my limited experience with the language I feel confident saying that in a lot of cases in which we see the use of Katakana, there is either no replacement Hiragana or Kanji that exists to replace the word (on account of the thing being not native to Japan), or it was "felt" that the word used to describe something is better written in Katakana (which is where those of us who look into this phenomenon get confused because this procedure as far as I can tell from my limited exposure does not make that much sense and it is unlikely that this was done methodically).
The first category I mentioned is pretty straightforward, things such as Chocolate or Soccer were introduced to Japan later on and thus the language needed to adapt to this expansion and that is where Katakana came in. A similar phenomenon (although not the point of a new set of characters) exists in many european languages, such as my native turkish, where for previously non-existing things we use the Turkish way of pronunciation such as "Telefon" for telephone or for some things that did exist, the european term has replaced the original one, such as "magazin" (magazine) which was called "mecmua" in olden times).
The case of ヘイケガニ is, however, truly baffling. Heike (or Taira) is a word that has historical significance in Japanese as it is the name of one of Japan's oldest samurai clans. Written in Kanji, Heike is 平家, which can be literally translated as "the house of taira" a clan name that was bestowed upon certain ex members of the imperial family. Descendants of Emperor Nimmyo, Montoku and Koko for example were given this clan name. The crab (Kanji 蟹 ) has also been known and consumed in Japan throughout its history. What could be the reason, then, that the Heike crab was given a Katakana name which is primarily used today? Curiously enough, ヘイケガニ is not the only crab species which uses katakana, but it is the only one which has a specific name identified with it. カニ is used instead for ordinary crabs, however one would think that a crab species native to Japan whose origins predate the use of kanji and has the name of an important clan attached to it, would also have a hiragana or kanji term.
Whats more, there is a rich history and an amazing legend connected with ヘイケガニ in Japan. As told in the Tale of the Heike (平家物語), a historic sea battle named Dan-no-ura (壇ノ浦の戦い) occurred off the coast of Honshu between the forces of Heike clan (led by the child emperor Antoku) and the Minamoto (Genji) clans (led by Yoshitsune, whose older brother Yoritomo consequently became the Shogun which marked the beginning of the Kamakura period). It is worth noting that this was also the battle where the 3 Sacred Treasures of Japan (三種の神器) were almost lost forever, tossed into the sea by the Heike clan as they were about to be defeated, but 2/3 were recovered with the exception of the sword which was lost at sea. For all this historic significance, this battle among these clans has a very important place in Japanese history.
Realizing they were defeated, the leaders of the Heike clan decided to end their lives honorably and threw themselves off the decks and were drowned at sea. This is where the folk-belief comes in, as it is generally believed that the ヘイケガニ appeared off the cast of Honshu right after this battle, as the reincarnations of all the samurai who drowned themselves at sea.
This event that occurred in 1185, and the belief connected to ヘイケガニ since that period, why is it the Heike crab is now written in Katakana? It is a mystery. The use of katakana for ヘイケガニ does not seem to have anything to do with the history of heike, and this just seems to be an oddity in the language. I am sure there are many other quirks like this in the use of katakana in Japanese, though for now, I would be contented knowing the reason behind just this one case.
