((Backdated to a couple of days after Katou comes back))
Once Katou was well enough to walk about on his own, he did exactly that. As cool as he was trying to act, it was really all too much for him to take in at once, and he needed to get away from Kira and Setsuna for a little bit. Which one he needed to get away from more, he wasn't sure of.
He had seen his Kira die, and he had seen Lucifer rise up. He had seen Lucifer kill his colleagues, and he had seen the look in Lucifer's eye when he cut through him, both times.
Setsuna was different. Back with his Setsuna, he had been able to read his thoughts, and read his emotions, and read everything. He had almost become an extension of Setsuna, and he had been happy with that, because he could always tell how Setsuna was feeling, and what he needed, and where he was. This wasn't his Setsuna though. He couldn't feel anything but the boys bright aura. It scared him, and made him feel lost, and made him realize that he needed to branch out a little bit and get away from him for a while. Though Setsuna was still Setsuna, and he'd protect him to the death, and he'd love him more than anyone else (except maybe Kira, though the two of them were pretty close), Katou needed to get used to the fact that Setsuna wasn't his Setsuna. It didn't change his feelings, but it would need to change how he expressed those feelings.
Besides, getting to know the park was something he needed to do to feel comfortable. He had just come from a very intense war, and he wouldn't feel right until he was completely comfortable in his surroundings. Though it still hurt a little bit to walk, and he often had to stop to take a rest, he told Setsuna and Kira he'd be back, and set out towards Toon Town - the place Mickey said he had lived - and he'd hopefully get to know who lived in the park, and who was a friend, and who was a foe.