Hane Hari no Kimi.
This Gothic shojo manga is a single volume comprising three stories -- a main one, "One with the Glass Wings," and two shorter stories "Firefly" and "Jion Princess" -- that feature characters falling in and out of love, against all odds. There is a fragility to the main characters in each story; each is afflicted with some sort of physical and/or mental ailment -- for instance, a blood disease is the affliction in the main story. But regardless of all the obstacles and interference, love conquers all.
(Source: Tokyopop)
