The manga, which has sold more than 65 million copies in Japan, revolves around three high school students: schoolgirl Minami - played by Nagasawa - and her childhood playmates Tatsuya and Kazuya, who are identical twin brothers and talented baseball players.
They share the same dream: to have their school's baseball team qualify for the national high school championship tournament at Koshien Stadium.
The manga - packed with the drama of sport as well as the excitement of secret love - is so popular that Minami is a household name among many comic and baseball fans in Hong Kong and Taiwan.
Playing a classic manga character is no easy task, said Nagasawa, who recently visited Hong Kong to promote the movie.
'Touch is a very popular manga and many people have a preset image [of how the story and the characters should look like]. It's a challenge to maintain the familiarity of the character while giving the role a fresh angle.'
The success of Touch owes much to its touching and accurate portrayal of sibling rivalry and brotherly love, which is said to be inspired by Adachi's own experience with his elder brother - a fellow comic artist who paved the way for Adachi's success.
Nagasawa witnessed the complex and intimate bond between brothers through working with real-life twins Shota and Keita Saito, who play the siblings.
'They rowed over some minor things during the filming. But you can sense that they are twin brothers, as they always share the same world, whether at home or on the film set.'
When it came to the movie's emotional scenes, Nagasawa said that Adachi's manga was a source of inspiration.
'It's quite difficult to act sad and do crying scenes. You need full concentration to do them well,' she said.
'But the scene [about a character's death] is portrayed exactly as it appeared in the manga, so I was able to seek reference from Adachi's work.'
Nagasawa first appeared in the limelight at age 13 after beating 35,000 contestants to become the winner of Japan's Toho Cinderella contest, which promotes up-and-coming talent.
She won an award at the 28th Japanese Academy Awards for best supporting actress in Crying Out Love, In the Centre of the World and is set to play the female lead in Rough, another youth manga by Adachi.
Nagasawa said teen romance, which has many restrictions, was particularly interesting.
'Touch, Crying Out Love, In the Centre of the World and Rough are all stories about youth. I think I can only interpret that feeling [of youth] during this period' of my life, said Nagasawa.
'If you are in love with someone, that feeling is different for a teenager than it is for an adult. I enjoy the feeling of being between the two.'
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