There are 2 writing systems is japanese, sound based and meaning based.
There are ~50 sounds in japanese language so when the writing system was originally created they assigned a Chinese character to each of their sounds. 安=”A” etc.
it was pain in the ass to write those Kanji and only noble male were using them so over time they developed something simpler call the kana 安->あ/ア
Hiragana is used for native japanese words and katakana is used for foreign words,
Kanji (Chinese characters) is used to decrease the number to characters they have to write and based on context can mean different things i.e.
最中 is a type of snack (meaning based-monaka) or currently (sound based -saichyu)
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