And I'm glad you liked it.
All right, about the big blocks of text, that's a bad habit of mine. I'm trying to break out of it, but it's probably still going to take a while. I'm going to write next a mission from back when he didn't have a partner as an execise for that - without anyone to talk to, I'm forced to keep his mouth shut and use more action than dialogue.
About him and Nikki being hard-hearted, here's why:
Nikki: She's a Sakura replacement I took from a fic called "The Final Ever After". I was going to kill this fic at first, but as I wasn't able to figure out what was it supposed to be I dediced to leave it alone (although I got there the inspiration for Nikki). She had quite of a rough time during it, in fact the PPC world is less grim than the one she's from.
Sergio: You were almost right with your deduction - he does suppress his own emotions as much as possible during missions. This time because he was focused on getting her training done as professionally as possible not only for her own sake, but also because he was in trouble with Upstairs due to his "screw rules, I'm doing the right thing" attitude. In fact, getting fed up with whatever was happening to Sakura caused him to kill several badfics before having gathered all the necessary charges (Mission #1 and #2 are two of them). However, it's already shown in those that Sergio manages to (barely) keep his emotions in check even without that reason.
I'm going to spoiler his backstory to explain that.
Sergio was from a massive crossover I wrote with some of my friends several years ago. During that time he was a borderline Stu and fell in love with Sakura, causing her to get in troubles only for him to save her, without knowing it. Sergio and his friends fought a lot of battles against a bunch of villains, always managing to foil their plans. At some point, Sergio&Co. were in a future where the world was controlled by the villains, in order to discover their plan and so be able to counter it in the present. Then things went haywire. The villains managed to kill Sergio's cousin leading to Sergio's sister despairing. We stopped writing short after that.
However, the battle continued. Sergio's sister, due to her unstable mood, got killed too. Since she was the one with the time-control power, the others were stranded in a bad future, and while attempting to overthrow the villains all of Sergio's friends got killed one by one.
In a desperate action, Sergio managed to plant a bomb at one of the villains' meeting, killing them all in one go.
The world was saved (but not safe, as there was no government), but Sergio was completely alone. Having somehow discovered the existence of Mary Sues and realized that he was a Stu himself, he began hunting them with suicidial perseverance, and got discovered by the PPC just before this vigilante life killed him.
He now tells everyone an altered version of the truth, claiming to be a clone of... well, himself, since he wants to forget all of that. Especially the fact that his previous Suvian nature ended up putting in danger (and eventually killing) the girl he was in love with.
He tries to block out emotions and memories of his pre-PPC past, since he thinks that they are dangerous to the people around him. And was working, as his lusting over Sakura steadily faded over time. (And, since he is now (2011 HST) 19 and Sakura's 10, it's a good thing)
The problem now is that he's partnered with basically a 16 years old Sakura, and that will bring out a past he wanted to forget.
Damn, I wrote a lot and I'm not even sure I managed to say all.