There's a lot of very hard things that Tetsu has had to do in "Lyra's Magnum Opus". He's had to accept Sana's limitations as they develop. He's very open to these changes and never judges, but they can be emotionally hard. For example, one of the hardest things was when Sana wet their bed, because he physically couldn't get up to go to the bathroom. Tetsu woke up from it, and his first instinct was to comfort Sana, who was of course very emotionally distraught and embarrassed. They'd been sleeping in a room with Tetsu's parents, so his parents quickly found out what happened. He only wanted to protect Sana's emotions and dignity, so he carried Sana out of the room to get him cleaned up. He later broke down about it, because he was so worried about Sana's emotional well-being, but also what it meant about Sana's developing terminal illness. Tetsu's family was very supportive and never spoke of it, cleaning it up for them and making it seem like it never happened. But, it's just one thing in many things. Tetsu bathed Sana after that, trying to smile for him and saying he's peed the bed as an adult also and that it was nothing to be ashamed of. But, Sana emotionally was dead to the world, so it was incredibly hard for Tetsu to see him that way. It was a break in Sana's usually innocent and pleasant demeanor, a window into a darkness that Sana possesses about his illness that Tetsu had never seen and that Sana tries to hide from Tetsu all the time to protect him.
