Complex sentence: Though he has little affinity for the trophy itself, he cherishes the memory of his victory over Kenzaburō--though he told Kenzaburō his victory was due to luck, he personally believes he won was because he was stronger than his senpai.
Split into simpler sentences: Though he has little affinity for the trophy itself, he cherishes the memory of his victory over Kenzaburō. Although he told Kenzaburō his victory was due to luck, he personally believes the reason he won was he was stronger than his senpai.