Watch Kosaka's sister send her message.

Riverside, California (CNN) -- Akiko Kosaka, a student from Japan attending the University of California at Riverside, had lost all hope for her family in Minamisanriku, the fishing village where more than half of the 17,000 residents are missing and feared dead in the aftermath of last week's tsunami.

For three days, she scoured the Internet. She received one e-mail that her youngest sister, Yukako, 13, was likely safe in her middle school's shelter. But what about her parents, paternal grandparents and older sister, who all lived under the same roof?

When the mayor was quoted in the media as saying he barely survived the tsunami, Kosaka thought the worst, because her father's pharmacy was located near the town hall.

"I didn't think they survived," Kosaka, 20, told CNN during a tearful interview Tuesday. "I cried for three days -- Friday, Saturday, Sunday."

Then she received word Sunday night from a friend in Japan of the existence of a 45-second YouTube video showing her family home as the only one standing amid the rubble. The video highlighted her older sister holding a sign to a TV news crew saying in Japanese "we are all safe."

Kosaka expressed relief upon hearing of the video, but became distraught after she couldn't find it online, despite staying up all night looking for it.

Then a contact through a Japanese social network e-mailed her the link Monday morning.

When seeing the video for the first time inside the home of her host family, Kosaka's reaction surprised everyone in the household.

"I screamed, and my host parents woke up and they thought it was really bad," Kosaka said. "They asked what happened. And I said, 'They survived!'"

In the video, her 24-year-old sister, Shoko, is standing on the family home's balcony, off Kosaka's bedroom, and is asking the TV crew to pass along word to her sister in America that she's safe.

Now Kosaka is trying to respond by using the media and the Internet to inform her relatives she's aware of their message -- though she's still concerned about them in the obliterated coastal village, which media accounts liken to a ghost town.

Kosaka has yet to see her father, Katsumi; mother, Noriko; or paternal grandparents on any video -- or receive any word from them.

Though she speaks English, Kosaka extended a message to them, in Japanese, through a CNN news crew: "My older sister, Shoko, I saw your video. Thank you very much for being alive. It made me really happy that you are worried about me even in this tough situation.

"Grandpa and grandma, how is your health? Dad and mom, I know that everything is tough right now with your job and everything but I am so glad that you are alive. I really look forward to seeing you guys again."

In the offices of the University of California at Riverside Extension program, where she began a year-long study of English last September, Kosaka provided a personal narrative to the stark footage of her hometown street now in ruins.

Kosaka's family home is the only one left standing on a hill because her father reconstructed the two-story house with a basement five years ago, Kosaka said. The other houses in the neighborhood were aging, she said.

Kosaka expressed shock that the earthquake or the tsunami demolished the block because she thought the area would be safe on high ground, she said. Her family's house has a scenic view of the ocean, just a five-minute walk away, she said.

In the video, a news crew approaches the family house, and Kosaka's older sister is wearing a white helmet and holds up one sign saying, "Kosaka Family," and then another saying, "We are all safe."

At another point in the video, the older sister indicates she's holding up the signs to the camera crew "because my younger sister is in America. We are all okay."

When Kosaka heard of the video's existence, she thought to herself, "I couldn't believe it. It's a miracle," she said.

Since seeing the video, she watched it over and over again -- at least "50 or something" times within about 24 hours, she said, offering a wild guess.

As she reviewed the video again Tuesday morning, Kosaka was still incredulous.

"This is my house," she said, viewing the video on a university office computer. "When I saw this video, I was very shocked by it. I thought (the hillside community) was safe. There were houses next to my house, but they were destroyed. That means the tsunami came up to the house."

She was moved to see her sister shouting to the news crew from the balcony. "It makes me very happy," Kosaka said. "It's the only way to hear her voice."

Her sister's voice, though, struck Kosaka as "tired and depressed."

"Maybe she tries to stay strong for my family. So I'm very proud of her," Kosaka said.

She believes her parents are likely OK, but her grandfather, Yoshio, is 85 and grandmother, Soyoko, is 80.

"My grandparents are old, so I'm worried about their health," Kosaka said, adding no one in her hometown probably has water, and the winter weather is still cold, with snow.

She's also worried about the family pharmacy, where her father, 52, is a pharmacist and her mother assists. The family opened it 10 years ago.

"I think it was his dream," Kosaka added.

Since Kosaka saw the video, she has been sharing her story with classmates. "I cried in front of them too much," she said Tuesday.

The University of California at Riverside Extension is the continuing education branch of the university and has an enrollment of 4,000 students from 60 countries who participate in English-language study or certificate programs, said Bronwyn Jenkins-Deas, associate dean and head of international programs.

Of the 4,000 students, 109 of them are from Japan, and five of them had families affected by the quake or tsunami or both, Jenkins-Deas said.

It is only Kosaka, though, who has yet to have direct contact with her family, Jenkins-Deas said.

"The story is quite amazing," Jenkins-Deas added.