Kirstie
When Buffy was a sophomore, Jenny Calendar made her entrance to both Sunnydale and Giles' heart.
When Buffy was a junior, she couldn't kill her ex-boyfriend. So he killed Jenny. Buffy sent Angel to Hell, but Jenny didn't come back.
When Buffy was a senior, Angel came back. But Jenny didn't.
"Visitors" is a story of loss subdued. Giles makes a pilgrammage of sorts, distracting himself with the mundane even as memories and horrible questions haunt him. He mourns Jenny, but also the loss of a possibility that was never fully realized.