I can't make it simple, so I'll make it long.
To start off with, the climax of the episode was the song. I knew it was gonna be good, but what I didn't know was that it was gonna be SO heartbreaking. The song, the sounds of the instruments, the lyrics. Boy the lyrics...
It was extremely emotional, the entire song was. Goodness, the way Mafuyu sang it... Wow. What really got to me though, was when he said "I miss you." He sounded SO lonely when he said it. It was heartbreaking and it had my whole face covered with tears. He's been wandering around, building SO much sorrow up inside, which he was never able to let go of.
For me, this was, by far, one of the most emotional scenes I've ever seen in an anime series. Mafuyu expressed himself in ways that people only dream of being able to do.
He finally cried. All the sorrow he's been carrying around for so long, finally began to fade.
Not being able to cry sucks, a lot... Being able to express oneself by crying is one of the strongest weapons we as human beings can have. There's nothing shameful about it.
Amazing performance, so many feelings were let out and "it shook me to the core." It really did.
It was also amazing how the song Mafuyu was humming through the series was played on piano in the bonus clip with them being on the beach..