Assuming you do this with only fishing, it takes around 3-3.5 hours in game time to reach fishing lv 10 for the 50% bonus from level 10 talent. By the time you reach fishing 10, you'll have more than enough to hit 50k with only regular fish. This result was from only doing mountain fishing in the Spring.

RNG is very heavy if you decide to also go for chests. I've had as many as 3 diamonds in a row from them, to as bad as getting regular rocks or 1 bait multiple times in a row. If you do decide to go for chests, then I'd recommend gathering 50 wood to make a wooden chest near your fishing spot.

Most likely, you'll be able to reach 50k by level 9 fishing if you use the soup Willy sells, and catch Legend. Supposedly he shows up as long as your fishing is level 10. Can't confirm using soup at 9 works though since I've never tried myself.

It'd also depend on whether or not mushrooms/fruit bats are faster income than fishing since you could just sleep and harvest them.

Happened to see this while browsing for Tales of Destiny.

Unfortunately, I haven't played the game in quite a while so I don't remember city names, etc. I do remember taking the time to kill Leon to get this ending though. Instead of doing it with a save glitch, I just walked to one of the other towns and bought a stack of 20 Energy Bullets to kill him.