I would likely not meet many residents of Gensokyo mentioned in any of the games' plots, and live my days out as a regular human in a human village just as everyone else in this thread would because realistically they aren't going to risk their lives to get to meet their favorite characters.
You could either live a relatively boring life (to be fair, a Keine is fine too), or you could take the risk involved with one of the various available get-to-know-the-touhous routes and live a life of win...
I suppose there are three obvious routes for turning yourself into a youkai.
- I hear Reisen sells medicine in the Human Village every now and then.
Apply charisma and/or manipulative skills/flattery, ask her if she can arrange a meeting with Eirin, ask Eirin for help. (the "Eirin Eirin Tasukete Eirin!" route)
- Alice seems to have done it. Ask her how/if she can help. For optimal results (the ones that don't land you as random food) make sure Marisa or Reimu is there before you go visit her house. (the Rozen Maiden route)
- Yuuka is theorized to have done it. Go ask her. (the Suicide route)
If you don't want to turn into a Youkai, you could always beseech Keine (the one who seems to be friendliest to humans out of the bunch), Marisa (the one least likely to kill you, but most likely to get you killed), Reimu (who will help you in any way or form as long as you donate) or maybe even still Alice (tsundere can be abused :'D) for training/help to get started with the whole survive-against-youkai thing.
Oh hey, there's one more type of route.
Making friends with a friendly Youkai/bunch of Youkai and hang around them, thus leaving you with protection against evil Youkai AND potential training at the same time.
Like maybe a certain wind god shrine.
Or Cirno. Cirno would be hilariously awesome.
Getting ⑨ to like you would be painfully easy.
And everyone else in Gensokyo would spare you out of pity. SAKUSESSU!
...I actually know someone who would seriously consider the Yuuka route. lol.
I'd probably start out with the non-Youkai routes, then try the Youkai routes (excluding Yuuka :'D) and if all else fails, try hanging out at the wind god shrine.
If all fails, one can still make friends with Keine in the human village, mirite?