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Okay, I'll participate semi-seriously. Kanji (hanzi in Chinese) are some several dozen thousand characters borrowed from Chinese for use in Japanese writing. Maybe 3000 or so of them see reasonably common use, though n00bs will tell you that number is 1,945, cuz that's the number the government has officially established for use in public schools, in government publications, and in major newspapers (with exceptions all over the place, however).
They exist because Japanese got writing from the Chinese, and the kana are just simplified/abbreviated forms of the kanji (? is cursive ?, ? is abbreviated ?, etc.).
They continue to be used today for a few reasons:
1) Japanese doesn't use spaces, so kanji, which represent meaning, make things easier to sort out.
2) They've been used for so long they've become part of the Japanese cultural identity, and besides, they're damned interesting.
3) There are a lot of words that are pronounced exactly the same, and even more where the accents are different, but the kana would be exactly the same, and kanji make those words very easy to deal with in writing, and also allow you to summarize in a few characters what would take a long sentence to say and be understood (useful for signs, newspaper headlines, and a lot of other stuff).
4) Conservative politicians have encouraged a trend toward increasing the number of kanji for common use.
As for kanji being words/sounds/pictures/symbols, well, all of these are kind of the wrong way to think of them. The oldest kanji were pictures or symbols representing ideas. But these became simplified to where most of them don't look like the thing they represent. And today (and heck, for the last couple thousand years), MOST kanji are in a category where part of the character is the basic category of meaning and another part of it stands for the pronunciation. I like to use ? (prefecture, specifically Kyoto/Osaka), ? (like a seal or a symbol, originally one made out of wood or bamboo, but now means all kinds of seals and symbols), ? (rotting), and ? (attaching) to illustrate this. All are pronounced ? (fu) in the Chinese derived pronunciation (Japanese pronunciations include "tsuku" and "kusaru") and ? shows the pronunciation. ? has "bamboo" as part of it, ? has "meat" as part of it, etc. So there's a logic to memorizing many kanji, but that doesn't mean it's easy, because you have to learn the logic, and there are tons of weird exceptions.
How did I learn kanji? By studying hard. And anyone who tells you there's another way to do it is full of it, period.
As for what Jarvik7 and I said, well, he said that "Shimashitakatta" is wrong and it should be shimashitaka. Personally, I was confused, and wasn't sure if that person wanted to say "benkyou shimashitaka" (did you study? - polite) or "benkyou shitakatta?" (with the question mark there, did you want to study? - politeness needs a suffix, like maybe "no desu ka").
Anyway, I replied that "nannenkan wo" (????) is also strange, because it makes "nannenkan" (how many years) the object, in other words, "how many years" is the thing being studied, which doesn't make any sense.
Finally, that kanji. I can't see all of it, so I'm not sure. It might be ?(ho/tamotsu, preservation), but I doubt it. It could also be an incorrect ? (kei, promise/contract) or ? (also kei, but a very rare kanji that means carving characters with a blade, which would be ironic, yet retarded as a tattoo). It might not even be a real kanji, however. Kanji tattoos are a very bad idea, as, outside East Asia, few people in tattoo parlors know what the heck they're doing (and in East Asia, it would just be like tattooing letters on your skin!). I even saw a U.S. tattoo show where they had a Japanese guy in the shop to help with kanji tattoos, and HE messed up a girl's tattoo! It was due to poor English. She wanted "peace of mind," and he gave her ?? meaning "peace," but as in no war (and it's ?? in Chinese, so Chinese people will think she got it backwards, haha). ?? would have been the proper kanji, but still a lame tattoo.
Okay, way more info than you need, and it took me forever to type this, so I'm out.