亀 means 'turtle'

English speakers see cats and dogs as enemies, but the Japanese and Chinese perceive the dragon and tiger as well-matched rivals. The dragon symbolizes everything from imperial power and water to China itself, whereas the tiger represents earthly matter and India, also inspiring scads of expressions about risks. Meanwhile, both cranes and turtles are emblems of longevity and good fortune. Moreover, the crane appears in proverbs, paintings, origami, ceramics, fabrics, poems, Noh dramas, songs, folktales, and even math problems, as well as figurative expressions, whereas the turtle symbolizes slowness, wisdom, experience, divisiveness, ugliness, and sexual attractiveness.

Though the Japanese live longer than anyone, they pray for even more longevity—for humans and deities alike. These four auspicious kanji are associated with longevity, which is a natural fit for 亀 and 鶴; as one proverb has it, turtles and cranes live thousands of years. Meanwhile, 寿 means "lifespan" and "longevity" in words for those concepts and appears in many terms for milestone birthdays. Finally, because the pine represents long life, thanks to its evergreen needles, images of that tree abound at weddings and on New Year's cards. Similarly, twin pines symbolize a long, happy marriage.