To be honest I think sea creatures are at a disadvantage here, because unlike with cats, dogs and many other land animals we humans find it hard to empathise with sea creatures (I think I also heard somewhere that this has something to do with our biology). We know rationally that they must be in pain, but they look too foreign for us to relate to. That is why shark finning can be done with little regard or conscience, why people can consume live octopus and cook lobsters alive: their pain just does not register in our brains as much as other land animals. That is why I think this manhwa is so important, because it helps us feel their suffering be depicting them as humans.
Sorry this post is a bit long :)
Animals have to be humanized so we can understand they feel pain. I wonder, why don't people notice their cruelty? We aren't better than any other animal.