I want to visit Japan, but I cant read Japanese.

Is this a problem? I have a fear that when I visit Japan, I wont understand Kanji or really anything else, is it necessary to understand Kanji?

If your Japanese, and cant read English. Same issue with any other country, if you cannot read.

Nope in the big cities like Tokyo and Osaka and so on 100% of public transport and most big shops have english everywhere

Visiting Japan and not knowing the language isn't necessarily an issue, but it would be nice to know some basics of the speaking and reading to ensure you're not totally dependent on the sometimes present Englishor some random person off the street to translate.

If you'd want to take the time, you could learn the Hiragana. While it won't be perfect knowledge, it can help you to learn Kanji with something called Furigana above each Kanji. But i'd imagine if you just knew some spoken Japanese you could get around pretty well. I've heard that Japan has a pretty nice populous so I don't think they'd mind helping you. Just don't be too dependent on others i'd say.

Get a tourist phrase book. They have all the phrases you need to survive and usually have pictures you can point too.

I lived there for a year and a half. I didn't really learn the language and I couldn't read more than a few signs. You'll get by fine.

Well you should try learning the letters first. I learn Japanese for 6 years now and I've been in a few Japanese conversations. You should be okay after learning the three writing systems - hiragana, katakana and kanji :D