Phonetically pronounced "Aishiteru", 愛してる is Japanese for "I love you" or "I'm in love with you". Though this phrase is not used much in Japan, it is common among Americans, or those from other countries who visit Japan or speak Japanese.
"愛してる", or "Aishiteru" the westerner said to the Japanese girl. She was surprised. She had never heard the expression in her life.