The center of the map in his room has Berlin in its center.
They are both voiced by Kenichi Suzumura, as per cast reveal for Schwarzesmarken.
Irisdina's death might be too painful for him to take, and he intends to take the world with him. Either that or he's actually trying to subvert or exploit Allegiance for his own ends.
Yui and Yuuya are half-siblings.
Courtesy of Alastor Mobius Toth, who wrote Muv-Luv: Comet: leaked images from the Total Eclipse visual novel show Yuuya's mother sitting front of a Sharp-Dressed Man in a 3-piece suit, flanked by two Imperial Royal Guards officers. The implication is that Yuuya's father is also IRG. AMT then speculated that Yuuya's father was in America for a training program (Yuuya was presumably born in the late 70s at the earliest, which coincides with the F-4 Phantom's deployment in US and Japanese forces), and fell in love with an married Yuuya's mother. However, he was forced to return to Japan and marry a woman chosen by his family, so that the family line would be secure... resulting in Takamura Yui. Before he could sire any more children or return to his American family, however, he was killed in action. AMT was inspired to make this WMG after seeing one of Age's crossover April Fools pictures, entitled "My Little Sister Can't be this Samurai!", casting Yui as Kirino and Yuuya as Kyohei.
Speculate no longer. This image http://puu.sh/2UQmk outright says that they're half-siblings, both having Yuuya's father as their biological father.
Also, it turns out that AMT's speculation was based on looking at Total Eclipse, and considering what the biggest dick move Kouki could pull would be. That said, what actually happened is that Takamura Tadamasa and Mira Bridges fell in love, but Mira disappeared once she realised she was pregnant, as she was afraid she'd be used as leverage against Tadamasa. Tadamasa, heartbroken and disappointed, went back to Japan and continued his IRG career, got married, fathered Yui, and died during Operation Lucifer.