Japan Trip to Tokyo - Can i visit alone if I do not know Japanese?

I think it's totally fine. Never been there alone, but I always go there every year mostly with my mom. Basically, I took care of everything myself from looking for places to meals. Japanese people are pretty friendly. If you get lost, they will show you the way.

I suggest you to download Tokyo subway map on your phone, also use your google maps, google translate, and do your research

Yes! I've been getting around Tokyo just fine for a little over a week now knowing only a few Japanese words when I arrived ("konnichiwa", "arigatou", "sumimasen", "hai", and "iie", which means "hello", "thank you", "excuse me", "yes", and "no", respectively). Almost everything is repeated in English on trains and in airports, most signs in transportation stations have English translations on them (including English maps, I just took a picture of one and have been using it ever since without a single issue), and most natives I've encountered know atleast a little English, more so in the 25-45 age range. Many hostels have people pretty fluent in English working at them and there are many Starbucks, so if you suddenly need Wi-Fi, there usually isn't one too far away. Just make sure you sign up ahead of time, as they require you to do so for all Japan based Starbucks, here's the link: http://starbucks.wi2.co.jp/pc/index_en.html

If you decide to get a phone card at the airport with limited data (I got a 1GB data SIM card) make sure it's with Softbank. Softbank offers free WiFi at many places through out Tokyo for it's customers, I've used my phone as navigation several times and because I have a Softbank SIM card I rarely actually need to use data, it's great!

It's a bit difficult, especially if it's your first visit to Japan. Have you ever heard about Sakura house in Japan? You can contact them to have the best place to stay in Tokyo and I believe you can receive a lot of help from the staff there.
I'm a host family there but I'm not very good at manga, so I think I cannot help you much. Hope you have a great trip to Tokyo.

Hahaaaaaaa...If you two can click, then I think she would divert her manga interest to others. I can't really believe that manga would initially be her priority.    Just an interest?

Hi Noviyanti. Yes definitely you can get by fine speaking only English. If you need to take a taxi then just be ready to show the driver the address of where you want to go (in Japanese) and if you are taking the train, there are always ticket offices where normally someone can speak a little English. We always travel by train a lot and never have problems (my wife is Indonesian).

there are som great manga shops in Tokyo so be sure to research on google where they are. Also visit Character Street in the basement of Tokyo Main Train Station as many japanese and mangga and cartoon characters have their own stores.