Buying American stocks on 一般 (Ippan) or 特定 (Tokutei) instead of NISA. Is the tax part very complicated ?

I'm interested in buying a stock(American company), but it cannot be purchased under NISA and can only be purchased under Tokutei and Ippan.

What are the complications I'll have to go through if I choose either?

I'm a company employee and my company handles all my taxes/nen matsu chosei etc.

If I ever sell those stocks, will I have to make separate filing by myself if I get any profit from those taxes? (No paper work if I sell it on loss?

I'm using Rakuten Shoken and am not a US taxpayer.

Can anyone please advise.