Seto Kaiba didn't have the nicest memories. He had grown up in an orphanage, and when he had finally been adopted, his new father hadn't been the most… loving. After he had gotten rid of his father, he had to run an entire company, not that he wasn't good at it, but sometimes it got to be a bit much.
However, Seto had an anchor. There had been a constant through it all. His brother, Mokuba, always seemed to make his day brighter. Because of Mokuba, Seto hadn't been lonely in the orphanage, his father's abuse hadn't been too much, and he hadn't been overtaken by stress by now. The younger boy had turned around his negative thoughts on more than one occasion, and Seto was thankful for it.
So maybe, just maybe, those memories weren't so bad, after all.