A Doubleware (ダブルウェア) is a special kind of person compatible with the Real Digitalize technology. This allows them to be inside of virtual spaces for an extended time without suffering secondary effects. Such is the case of Tokyo Kuryuu, who was inside of The World R:X for the duration of the whole game as well as Lara Hoerwick who enters the game even more directly through The World's Epitaph Data.
Harald Hoerwick seems to have been the second human to fully enter the digital space, though it´s unknown if he did so in the flesh, his consciousness seems to be trapped in The World after he tried to reason with Morganna.
Tanaka Kakeru seems to have some sort of Double Ware like ability, since his eyes glowed, showing the symbol. He has been under Tokyo´s monitoring for a long time due to this.