The Loneliest One

"I swore I'd be by her side until the day she no longer needed me."

Kureno is described by Natsuki Takaya as being the loneliest member of the zodiac because Akito keeps him in isolation. That being said, even without being isolated by Akito's orders I have difficulty believing Kureno wouldn't still be lonely.

Kureno's loneliness stems from three points. The first is his age. Kureno was born between the older zodiac members and the younger ones. The oldest three members, the Mabudachi trio were a tight knit group leaving Kureno on the outside. The younger members are all at least seven or eight years his junior. The only other member of the zodiac who was born during this gap of sorts is Ritsu, who also doesn't seem to be close to any other zodiac member.

The second cause for Kureno's loneliness is his broken curse. While the curse was broken through no fault of his own, its breaking was a defining event in Kureno's life. The broken curse makes the other zodiac members instinctually wary of him and makes Akito overbearing. Beyond that he does not even have the comforting presence of the birds that used to surround him. He can't fly with them. Instead they now fly away from him.

Finally, and perhaps most importantly is Kureno's choice. Kureno's cage is one of his own making. He made a promise to Akito at a time when they were both desperate. It was his own self-sacrificing nature, however that made him keep his word at the cost of his own happiness. Kureno isolated himself because it was what Akito wanted and while he could have easily opposed her in this he chose not to. Kureno's personality and choices are the largest contributing factors to his loneliness in the end.