Hello.

I think it's very hard to stay in Tokyo for 2weeks with only €400.
Staying in Tokyo is the most expensive in the world.

Please see below

Tokyo Price Guide | Commercial Heart of the City

Surprisingly Cheap in Tokyo if you know What's What
 

The first thing I would say is if you are going over without much money, you need to have a backup plan. What if you miss your plane? What if your keycard won't work? Japan is a cash society so you'll need to carry some cash.

• Carry a Visa Card that you can withdraw cash from (last time I took a Mastercard, and 7 11 stopped taking this making getting cash very difficult)
• Ensure Relatives can top up your account if required
• Take travel insurance (including health - not negotiable)

I'd say go for a shorter time to have a better time.

When my credit card didn't work, I had to forgo the 5 star hotel I had booked and stay here: ACE INN Shinjuku-We are ACE INN, BACKPACKER'S HOTEL in Tokyo.

There was a share shower, and I did stay in the "luxury" section. Even though there was about 40 beds or something - only three were full on a whole floor, making it similar to having my room.

There was a share shower that cost a dollar or thereabouts.

Really - even though I am a 5 star person, it was definitely okay. I'd say you can pay $50 per night and stay at some okay places. Have a look on Trip Advisor (Ace Inn Shinjuku (Shinjuku, Japan) - Capsule Hotel Reviews - TripAdvisor. I really liked the Capsule Hotel aspect of Ace Inn Shinjuku - though some say it's overpriced, and the lower floors can be noisy, I found it to be a welcome home sweet home.

I also picked up about 5 unlocked wireless internet connections from the comfort of my capsule! There was a locker for possessions.

As for drinking and eating - well for some alcohol as a nightly relaxant, you can always start with the vending machines (just don't get feral - you're representing your country :p)

Food - well, really the first time, I didn't know how to order in Japanese, so I lived on 7 11 food, which can be healthy. Salads, tofu rolls (and then your sweet buns for just a few bucks each)

I'm talking Australian dollars / US dollars here (approximating $1 to be about 100 Yen)

I'd say carefully plan - because there might be places where your dollar would go further. If there's two of you, then perhaps you'd get better value from a hotel in a business district like Otemachi.

Around Ueno is meant to be some cheap hotels - but I found that they were overpriced and the one I stayed in was sooo dingy (despite okay reviews). Just not worth it.

Don't let a train trip scare you off. Five stops from Tokyo is nothing, and you need to know how to use the trains anyways.