They were in the hospital wing.
"Who are you?" Harry Potter said to Luna.
"You-Know-Who. Hiss hiss hiss," Luna said. She held fingers down from her mouth and swayed like a snake.
"This is Loony—" Hermione said, "Luna Lovegood. She created the BOY-WHO-LIVED GETS DRACO MALFOY PREGNANT headline the summer before last. She believes there exists an unobservable Platform Nine and One-Half concealed by powerful magics. She claims you and she adventured together without me."
"Do you have any evidence I trusted you before I lost my memory?" Harry asked.
Luna glanced at Hermione.
"All my secrets are hers as well," Harry said.
"I know your real name, that you're a Parselmouth and that you've operated the Mirror of Atlantis," said Luna.
"My real name isn't something I'd tell you so you must have worked it out yourself and therefore does not constitute evidence of my trusting you in the past. There are at least three people who know I'm a Parselmouth so it's not surprising the information leaked out. These are the same people who know I've operated the Mirror so the Mirror adds no bits of information. An enemy would be at least as likely as an ally to possess this information," said Harry, "Did we discover an ancient artifact or something?"
"We found the Lost Diadem of Ravenclaw together," Luna showed it to him.
"This crown proves little since you could easily retcon a story around it. On the other hand, there is information I would tell someone I trusted if I wanted to guarantee recognition in case of obliviation," said Harry, "Do you have the recognition code?"
Luna recognized the logic of someone whose priors outweighed the available evidence. She fled the room.
The Marauder's Map showed Luna how to climb on top of the Great Hall. She hugged a stone gargoyle at the edge. It guided her tears down into the Hogwarts courtyard.
"Not now, Wanda," Luna said, "I need to feel this."
Luna detected quiet behind her. She continued staring at the students mingling below.
"I do not intend to jump," Luna said.
"I do not intend to stop you," Lady Yue said.
They listened to the wind. They smelled the gentle scent of trees.
"How does one make friends?" Luna asked.
"That is Professor Lockhart's field of expertise," Lady Yue said.
"Do you have a spell for loneliness?" Luna asked.
"今夜鄜州月，" Lady Yue sang from her teenage youth, "閨中只独看。遥憐小児女，未解憶長安。香霧雲鬟湿，清輝玉臂寒。何時倚虚幌，双照涙痕乾？"
《月夜》 Moon Night by Du Fu 杜甫
Tonight Fuzhou moon,
boudoir inside only alone see.
Distant tenderness small girl,
unsolved recall Chang'an.
Scent fog cloud hair wet,
clear splendor jade shoulder cold.
When lean empty window curtain,
both shine tear stains dry.