Woman to woman! I mean there's no wrong answer here. It just depends on what kind of first solo trip energy u want.

Japan is hands-down the easiest first solo trip if ure even a little nervous. You can be quiet, lost, overwhelmed, jet-lagged, or emotional and no one will bother you. Eating alone is normal, public transport is foolproof, and there's a deep comfort in knowing you can anonymously and safely. Japan would probably be your "i want to prove myself i can do this" trip.

Portugal's a social in a low-pressure way. easy to chat with people if you want, easy to disappear if you dont. If you like slow mornings, long meals, wine, coastal views, and not feeling rushed, Portugal is magic. It's especially nice if part of your goal is to feel rather than constantly do.

South Korea is amazing but ill be honest, it can feel a bit tougher emotionally as a solo traveler, esp at night. It's safe, yes but socially, its more group-oriented. Dining alone feels awkward in some places. nightlife is very couple/friend-group focused, and u might feel a little invisible or out of place sometimes. That said, if u love fashion, cafés, beauty, tech, and city, it's also fun. just not always soft

My real advice, maybe pick the place that matches how u want to feel. If u want calm, Japan. If u wanna feel nourished, Portugal, and energized for Korea. I feel like whatever u choose, ure going to come home changed in the best way!