[Otomezuka, near Ishiyagawa St on the Hanshin line in Kobe]
This will shock modern readers: there seems to be no psychological justification for her suicide. Perhaps it is an extreme example of what the Japanese call "enryo," "deference to others." Unai apparently felt bad that these fine young men were fighting each other on her behalf and thought that she could solve the matter by removing herself from the equation. Rather than bring unhappiness to those who loved her, she ended her own life. (By the way, this situation is mirrored in The Tale of Genji, where Ukifune is unable to choose between Kaoru and Niou and decides to drown herself in the Uji River - without, by the way, succeeding for she is saved.)
But that was a miscalculation: both lovesick suitors immediately followed her in death...
The best poem version is by Takahashi no Mushimaro (active 720s-730s), who was known for his poems on travel and various local legends. As Edwin Cranston says in the introduction to his translation, Mushimaro recasts the three suicides in terms of flight and pursuit and so manages to convey the blindness of passion.
The Noh play Motomezuka ("The Sought-for Grave") goes one step further than the Manyoshu poem and Yamato Monogatari story by showing us the afterlife of Unai. A priest, who is traveling through the Ikuta area, meets the ghost of Unai and listens to her sad story. The landscape is suitable desolate: although already the season of picking the green spring-shoots, the Kobe countryside is still unnaturally bleak and wintry. We hear the sad story of Unai told by her ghost. She adds that she now suffers torment in Buddhist Hell as punishment for her "offense" (the "offense" presumably being that she was held responsible for the deaths of her lovers, an instance of the misogynistic side of the Buddhism). Despite the priest's earnest prayers, the ghost finally vanishes into the darkness of Unai's tomb, making a mockery of its location, "Ikuta" (which after all means "Field of Life"). Indeed, a sad and strange story...
[Another version of the same tale, called "the Maiden Tegona of Mama," is set in Ichikawa near Tokyo and has also inspired several Manyoshu poems.]
References: A Waka Anthology, Volume One: The Gem-Glistening Cup by Edwin A. Cranston (Stanford, 1993) contains a translation and discussion of the poem by Mushimaro; 20 Plays of the No Theatre by Donald Keene (Columbia, 1970) contains a translation of the Noh play Motomezuka. The Yamato Monogatari has been translated by Mildred Tahara as Tales of Yamato: A Tenth-Century Poem-Tale (Hawaii, 1980).