The writing system, all three of it
As hopefully evident, you and me both will have to go through learning three different writing systems. Let's go through them:
Hiragana
This is the official Japanese phonetic alphabet, consisting of 48 characters (including 2 that are no longer used). Each character represents a different syllable, and obviously not all sounds are covered
Katakana
The phonetic alphabet used for words derived from other languages, such as 'hamburger'. Also consists of a total of 48 characters (including 3 that are no longer used). It looks and feels simpler than hiragana, and also serves a purpose of modernizing specific aspects of Japanese (mostly sounds not included in the original alphabet).
Kanji
The pictographic alphabet, and effectively what keeps Japanese from being a relatively easy-to-learn language such as English. Many of the characters here represent either a word, or part of a word. They have usually at least two different readings each (which situationally change). On the average everyday situation, you would expect to run into ~3,000 of them, a fraction of a total 50,000+ characters.