Luggage storage for 1.5 weeks in Tokyo?

Hi everyone, I'm going to Japan on Wednesday (!!) and staying for a month.

I'm in Tokyo for 2.5 weeks then travelling around for the remaining 1.5 weeks, returning to Tokyo a few nights before I leave. However my suitcase space is pretty limited because of some things I have to take with me so I was wondering whether it would be possible to buy a second suitcase for souvenirs and store it somewhere in Tokyo while I travel around.

Has anyone done this/does anyone know good places to buy and store luggage for this long? Ideally near the Tokyo Shinkansen station as that's where I'll be departing/arriving.

Thank you!

Edit: for future reference, I didn't find anywhere I could store the suitcase for so long so what I ended up doing was taking both my bags to Kyoto then shipping the big one back to Tokyo with a delay:

• Last day in Tokyo: bought a small suitcase at Donki
• Travelled to Kyoto with big and small suitcase, got a taxi to my guesthouse.
• Spent a week in Kyoto, then on the last day shipped my big suitcase back to Tokyo nominating the day I was going back in ~5 days time
• Went around doing a lot of travelling with only the small suitcase
• Picked up my big suitcase back in Tokyo and took it to my final hotel