Thanks for the links Noheart, now back to topic
About Vergil caring for Kat in game, when I first played trough the mission where you protect him and kat while they set the order hq to expode, when Vergil first notices Kat he seemed suprised, after i replayed the level I noticed, he is relieved, i tought for a sec he would go and hug her had not Dante interrupted, tough that moment was ruined by his later "we can't save Kat lets just leave her to die without saying goodbye" moment, it still may forshadow hidden feeling.
About his true DT not getting used, remember the fight, Vergil just "playing around", smiling "I got dis sh*t under control" attitude, then the stab came out of nowhere, maybe he could have used his DT had he saw the need,but in the comic after kat passes: anger, rage "Im gonna blow up the world" attitude, or if this is not enough, if you played DMC 1, remember how Dante got his true form to fight mundus? Sparda's form? Trish's what seemed as death that led to dante's what? that's right: anger, rage "Im gonna blow up the world" Anger equals unlocking god powers i guess, like in Asura's wrath