The first one is because Tomoka's pinyin is "fgyy", which is equivalent to the homonym of "awsl" and "Ah, I am dead". It is a nickname for him by anime fans;
The second reason is that Tomoka loves radish salmon. The author said that Tomoka smiled while eating radish salmon, which is very rare for protecting liver and benefiting courage. He has always been very cold, so he left a deep impression on anime fans. Everyone called him a rich fish and also called him a fish fish.