Well, I hate to break it to him, but making new friends is harder in general as an adult.

I don't know if Pewdiepie managed to make new friends there, but from what I've seen in his videos, he's got a pretty friendly relationship with his neighbours. And how did he and his wife do that? By following Japanese custom and bringing them a gift, introducing themselves to them. He's also said that he's had no problem with people being racist to him and in his experience, if you make sure to follow the unspoken social rules, they will treat you friendly. And Pewds doesn't even speak Japanese all that well.