Using NISA for short term stock investment

[yum]

Hello all,
I’ve recently committed to improving my personal finance strategy and would appreciate your insights on my current approach. Below is my case study—any feedback or suggestions would be greatly valued!

Background
Age: 29, single, no debt.
Location: Tokyo
Income: ¥5.5 million/year (gross) as a software developer.
Emergency Fund: 800k
Goals: Build long-term wealth, optimize tax-advantaged accounts, and explore strategic investing.

Since last year I was new to this so I was inconsistent , this year I plan to max out my Tsumitate portion.

Current Investment:

• Tsumitate -> 1.1 million
  • Emaxis Slim S&P 500 (80%)
  • Emaxix Slim All Country (20%)

• Growth -> 500k
  • Currently experimenting with individual U.S. and Japanese stocks.

• Gambling -> 100k
  • Some Cryptos

Given my income constraints I cannot max out the NISA Growth account, I’m considering using this account for short-term trades (weeks/months). Is this wise, or should I prioritize long-term holds here? Also, my Tsumitate allocation is heavily U.S.-focused. Should I reduce S&P 500 exposure and increase the Emaxix Slim All Country portion? Thank you in advance.

[zeroshiki]

There is nothing stopping you from using the Growth portion like an extension of your Tsumitate and have long-term mutual funds there. In fact, that's the prudent choice.
You're quite young so I won't try to dissuade you from trying your hand at the market but my recommendation is to just use the regular taxable account for your "play money". If you accidentally buy the next NVIDIA, the 20% tax won't really matter anyway.