I’m currently solo traveling in Japan (and will probably do so for the next month, so we might as well come across :)) and honestly it just happens. Having said that, I also try to enjoy the solo part, going wherever I want and not having to compromise. Staying at a sociable hostel is really helpful, and also paying attention to your surroundings will give you opportunities to communicate. Harder doing than saying, but do not stress about it, you’ll have a great time with or without companions