Meeting an 'Old Friend'

"Who else knows about this?" After hearing everything, Rin just had to ask the question since it was all too important. If his son managed to stumble upon such crucial knowledge about the game, then there's a huge chance that some of the other Dreamers have also discovered the same thing and are now taking action about it. And if such wasn't the case, then at least a select few people in the World of Lucid are probably aware of it and are now trying to stop it. From what Yuuta said, the danger involves both worlds, so it's only fitting that both sides are taking action.