Did any writing systems, or even failed attempts at them, exist for Japanese before kanji was imported from China?
Does history belong on this site? Anyway, I just flickered through my history book and came up with this.
First off, from Wikipedia and common sense: Hanzi is said to have come into existence around 2650 BC. "Common people" didn't just go write things for fun "back in the day", that was something for the wealthy. (emperors and such)
Now, though legend says the first emperor of Japan lived around 600 BCE, the first recognized by text is princess/queen/empress(?) Himiko, written in the Chinese text Weizhi around 297 CE. The first text to recognize Japan at all is a Chinese text (Hanshu) written around 87 CE.
A prince Shootoku is said to have written the first Japanese "constitution" at 604 CE. An image of Chinese text is given, though it's not saying not much about it.. Around this time is also when Japan started to record its own history in text. Nothing is mentioned about what writing system they had, but Japan was influenced a lot by China and Korea. The constitution itself was merely some Buddhist guidelines, meaning Chinese text was reasonably imported along with Buddhism.
The first Japanese collection of poems, Kaifuusoo, was given out at 751 CE. Here it says it was written in Japanese, though with Chinese characters because they didn't have their own writing system yet. Some characters were used for their meanings, others because their readings resembled the Japanese words.
..not exactly conclusive evidence, but it's something, and too long to be left as a comment, so here we go. I guess they could still have had some primitive cave-like drawings, but I don't know if that's technically classified as text by linguists and such.
There are some dubious claims collectively called 神代文字. The dominant view in academia is that these are fake.