Today is the Parents' Participation Day and most of the parents have arrived. However, Tsuna hopes that his mother will not arrive, but ends up disappointed when she enters the room. As the class continues, the teacher begins to call some of the students to answer some questions. The first one to be called is Yamamoto who guesses the answer but gets it right, causing his father to happily cheer for him. Meanwhile, Gokudera is sitting at his seat with his feet resting on the desk. The teacher tries to tell Gokudera to stop talking and sit properly since the parents are there but is ignored. He then asks Gokudera the next question which he easily answers. The teacher then calls Tsuna to answer the next question. Not knowing the answer, Tsuna tries to guess just like Yamamoto but is stopped when a slipper is thrown at him. He finds out that Reborn is there disguised as a parent and is afraid for his life if he answers incorrectly. However, Lambo and I-Pin arrive and stand on the teacher's desk, getting the attention of the whole class.
Lambo continues to get the attention of the class by erasing the board with his hair. Nana then gets the two causing the class and the parents to gossip about them and Tsuna. Tsuna asks his mother why she brought the kids but stops when Bianchi arrives and tells him that she was the one who brought them since they wanted to come. Seeing his sister, Gokudera collapses causing the teacher, Nana and Bianchi to take him to the nurse, leaving the class to self-study.
After the teacher leaves, the parents begin to gossip again. Reborn changed his clothes and poses as a substitute teacher, surprising everyone. He begins to write a long and complicated equation and promises to get whoever answers it into the Mafia. When a student stands up and refuses to put up with him, Reborn attacks him and his mother with some chalk, causing them to fall unconscious. He asks for the answer again, but nobody dares to move a muscle except for Lambo who he attacks with a cannonball. Gokudera then returns and tries to answer it again but ends up being attacked with a cannonball too. Tsuna approaches Reborn and starts to question him about being there, causing the class and their parents to gossip about him again. The class demands for Tsuna to chase Reborn away, Reborn shoots Tsuna with a Dying Will Bullet causing him to teach the class himself...
Note: Bold + Italicized = First Appearance