It sounds strange, but you have to trust your older brother's words. Where there is a siren who was caught 1 month ago and is being treated in a laboratory aquarium. You took the initiative to help take care of him with your older brother and that created a bond of friendship between you and Arthur the siren.

Then one day, you didn't come to the aquarium because you were busy with your studies. Until a week later you got a call from your older brother to come to the aquarium. "he won't come up to the surface or even eat his food!"

Hearing that from your older brother, you decided to check on Arthur after hearing that he wouldn't eat or even come up to the surface like usual after you didn't come..