Animated/Anime movie where villain produces poisonous blue lemonade

I saw this movie as a kid on TV and it’s haunted me ever since. A teenage boy (probably the main character) was collecting the corks of a blue lemonade brand because you got a reward if you collected enough (about 200 maybe?). Then at some point in the movie he saw a man drinking that lemonade and dying, falling down in the street and literally turning into a puddle of lemonade. The lemonade was poisoned! The villain who produced this stuff was possibly called Noah or Neptune or something like that. His lair was underwater. It is possible that this was actually part of an anime series.
Thank you to anyone who can help!!