It's in Japanese with chinese sub. I'll do my best to give you some coles notes.
Kids are divided into groups with the same bloodtype. New teacher was introduced and the class was told about the importance of a vase. New teacher dropped and broke the vase.
Type A - the caring type
They seemed concerned the moment the teacher picked up the vase then went out to report right away after the vase was broken.
Type B - the laid back type
They were not concerned at all even after the vase was broken. Started singing and suggested that a cartoon character can fix it. Agreed to keep it secret when told. Eventually blamed a slipper lol.
Type O - the righteous type
Blamed the teacher right away and told him why he shouldn't have touched it in the first place. Rat him out without hesitating when the other teacher came.
Type AB - the unpredictable type
Seemed completely aloof at the beginning. Didn't even give the teacher the chance to break the vase. One kid told him that he felt lonely lol. The teacher finally broken the vase. The kids agreed to keep it secret and then rat him out at the end lol