In episode 5, Wataru tries to perform a violin concert in his house to show his neighbors that he's trying to open up and be more outgoing. He fails miserably, but in the next episode he is able to perform for Megumi in her hospital room.
Otoya's belief that every person has their own special "music".
Otoya performing some magic tricks in episode 7 while he and Yuri are trailing Jiro.
...although it causes them to lose him and he gets beaned in the head with a rock for his troubles.
Wataru manages to overcome his shyness and sing in front of a group of people as he is performing along with Kengo, Shizuka and Megumi.
From the same arc, after Kengo says they could be friends, Wataru is so happy he seems like he's about to cry. Considering his lonely life until there, it's so sweet.
Dai-chan/the amnesiac Rook carrying Wataru on his back after his leg goes numb.
Otoya teaches the young girl that inspiration and wanting to play the violin are more important than trying to meet her parents' expectations. She manages to pass her audition even though one of the strings breaks on her violin. She later quits playing the violin because Otoya teaches her to listen to her own heart and follow her own path in life. She later becomes the Olympic archer Mami who Wataru meets in episode 17 and 18.
The relationship between the Fangire husband and human wife from episodes 23 and 24.
Otoya finding the ring that Yuri lost as a child.
In episode 36 a group of neighbors gather at the gate to complain about Wataru's constant violin playing causing too much noise. Shizuka begins to apologize for him when, to her surprise, Wataru walks outside and apologizes to the group himself, showing how much he has grown from the eccentric and reclusive young man he was when the series started. This also surprises the neighbors, who then realize that they have been rather harsh towards Wataru and then become more friendly with him.
Taiga letting Mio escape, even though she just tried to kill him. She later returns the favor, by taking an attack meant for Taiga.
After Wataru returns to his own time, Maya comments that Otoya acts brave even though he's in a tremendous amount of pain from using Dark Kiva.
Maya: You put on a brave face, even though you're in enough pain to die.
Otoya: I don't want my face to look wretched in front of my son.
The arm from the 1986 IXA armor that was destroyed when Wataru and Otoya destroyed King saves Wataru when the newly-revived King throws him off a cliff in 2008.
Nago trying to set one of his bounties on the right path after the man tells him how meeting with Otoya destroyed his life. He starts crying, so Nago hands him his handkerchief.
Nago: You blame your sins on others. Please overcome that weakness.