During his stay in Asgard, Damien has learned many things because of the similarities and differences from his home world and this one--but mostly because of the people he interacted with. Back in his home world, everybody was nice to him because he was essentially like a bomb that was carefully placed in a sealed box. Because of that, they had to be nice. This was why Damien really never found conflict with him as the center back home. However, when he found himself in Asgard, people no longer had the obligation to be nice to him, which was when he noticed the huge differences as to how people acted back there and in Asgard. So basically, he wasn't just spoonfed things all the time ever since he came to Asgard and started acting on his own based on what he knew. As a bonus, he was no longer with his caretaker, so he believed that he could do anything he wanted and that nothing bad would happen to him because the fact that the people in Asgard were not as nice as the people back home did not quite yet sink in. So when he encountered Kanone during night time, it hit Damien pretty hard and that maybe, just maybe, he should be more cautious of what he does around Asgard. He can't just do whatever he wants without consequence and this event helped him realize that and have that fact sink in.

Prior to Asgard, Damien has been wary about meeting strangers. However, due to circumstances, Damien had been forcing himself to talk to other people he didn't know. It was mainly due to the letter he was given as his welcome to Asgard. It gave him a sense of duty because he was needed for something. Therefore, he took his time to talk to others and built up relationships with others. With this, he learned that there were many different kinds of people out there and in his mind, he slowly learned how to deal with them: the sensitive, the loudmouths, the rude ones, etc.

Over time, Damien gradually changed from the person who was always watching everything to the person that was always doing something. That is to say, he doesn't get involved with every single thing, but he does participate in more events than what his former self would have back home. For example, Damien helped set up Arbor Day with Hanako Ikezawa. Even though it started off as an idea, Damien and Hanako went through with it. At first, he was afraid that nobody would take him seriously because he's a child, so he worked harder to make up for the fact and wanted to seem more reliable instead of being the casual bystander that he was before.

Also, hanging out with specific people such as Koyuki Sasamori and Sophie has been driving him a little further away from pessimism. This also ties in with the "nobody will listen to me because I'm a kid" point earlier, because if this was the earlier Damien before he came to Asgard, he would have given up on the spot. But now, he thinks it's worth taking a chance, because you never know what would happen, right? Right. Since he is still a child, he is still prone to copying traits due to much exposure, so this played a part with the lessening his pessimism.

Basically, Damien changed from a kid who always watched others from the sidelines to somebody that is getting involved with things if he could help out while learning more and more about different kinds of people as time passes.