There are a number of shows/manga where characters have names that are English words. In Vampire Knight, a character is named Zero. Tokyo Mew Mew has characters with names like Lettuce, Mint, and Berry. Is there a tradition behind this?
There can be numerous reasons justifying the usage of English names. I would divide them into two categories: plot reasons, and non-plot reasons.
The plot reasons are rather obvious, and include (but not limited to, of course)
- Some characters were born in non-Japanese-speaking countries, disregarding where the story itself is happening. Note that those are not necessary English-born characters or English names. For example, most names in Code Geass, Hugh Anthony Disward from The Mystic Archives of Dantalian, Victoria Seras from Hellsing, and so on and so forth.
- Sometimes the setting is a future world/alternative history/another planet/imaginary fantasy world. This can also justify such names, because the characters were born in a completely different culture that has nothing to do with Japan. For example, Cowboy Bebop, Trigun, Spice and Wolf, FMA characters.
The non-plot reasons would be:
- The name looking/sounding cool or pretentious, for example, Zero.
- The name meaning or symbolizing something, like Riza Hawkeye, who is a sniper, which her name suggests.
- Some other special cases. For example in Detective Conan the names were changed in the English version to make it more attractive to the audience.