The easiest way to do this is to let the AI battle for you. You could always select the novice tower and play 125 times (625 total battles) or you can select your character and hit
to turn on AI mode and just randomly hit
everytime the battle ends to start the next fight while watching a movie or doing something else. This will be a grind but if you are doing other things at the same time it came by quicker than I expected. Both klassic towers and the time trial towers count towards this. Some of the towers in time trials are actually a single battle long. Others are up to 8 fights so bouncing back and forth might make this slightly quicker.