「星のカービィ」- Why ィ and not ー?


The Nintendo character Kirby's name in Japanese is 「星のカービィ」, pronounced "Hoshi
no Kābī". For the カ, a ー is used for extending the vowel sound. For the ビ,
though, a small イ is used.

I thought the small vowels were used for modifying the vowel in an existent
sound without extending it, for example in ティ, to make "ti", or in ヴィ, to make
"vi". With ビ, however, that is of course not necessary, as the vowel is
already "i". In hiragana, normal vowels are used for extension, but those are
1) not small, and 2) not used in katakana.

So why is this? And how does it work? Under what grammatical rule does the
small vowel extend the sound, and why is ー used for カ and not for ビ (which I
think it normally would, such as in 「ビール」)?




When a small vowel is added to a kana with the same vowel sound, it does
indeed work the same as a [長音符]{chōonpu}. (If the kana has a different vowel
sound, then the sound is not extended.)

There are no hard and fast rules about this, but it seems that the ィ here is
used in proper nouns to indicate that the English spelling ends with "y"
instead of being written "ii", "i" or "ī". Other examples include

  * [ラッキィ池田](https://ja.wikipedia.org/wiki/%E3%83%A9%E3%83%83%E3%82%AD%E3%82%A3%E6%B1%A0%E7%94%B0): Lucky Ikeda, a comedian
  * [ファジィ論理](https://ja.wikipedia.org/wiki/%E3%83%95%E3%82%A1%E3%82%B8%E3%82%A3%E8%AB%96%E7%90%86): fuzzy logic




When a small vowel is added to a kana with the same vowel sound, it does
indeed work the same as a [長音符]{chōonpu}. (If the kana has a different vowel
sound, then the sound is not extended.)

There are no hard and fast rules about this, but it seems that the ィ here is
used in proper nouns to indicate that the English spelling ends with "y"
instead of being written "ii", "i" or "ī". Other examples include

  * [ラッキィ池田](https://ja.wikipedia.org/wiki/%E3%83%A9%E3%83%83%E3%82%AD%E3%82%A3%E6%B1%A0%E7%94%B0): Lucky Ikeda, a comedian
  * [ファジィ論理](https://ja.wikipedia.org/wiki/%E3%83%95%E3%82%A1%E3%82%B8%E3%82%A3%E8%AB%96%E7%90%86): fuzzy logic

