One main element is his difficult upbringing in poverty - stricken surroundings. Another is the constant bullying and discrimination he endured due to his physical appearance. And of course, his strong bond with his sister Daki. This bond was what drove him to protect her at all costs and also influenced his actions as a demon. For example, he would go to great lengths to avenge any harm done to her because of their shared experiences of being outcasts in society.
Gyutaro was born into poverty. He and his sister Daki had a very tough life. They were constantly bullied and looked down upon. Gyutaro had a deformed body which added to his misery. He was filled with hatred towards the world that treated them so badly. In order to protect his sister, he became extremely violent and cruel to those who he thought were threats. His experiences in his early life shaped him into the demon he later became, using his powers to lash out at those he despised.
Some of the popular baby games in cartoons include peek-a-boo. It's simple yet engaging for little ones. Also, puppet shows are sometimes depicted as a form of entertainment for babies in cartoons. These games make the cartoons more charming and relatable for young viewers.
It could be related to the story's setting or theme. If it's not a dairy-focused comic, there might not be a need for a lot of milk. Also, it could be a way to add an element of scarcity or challenge for the characters.