A Dictionary of Mutual Understanding de Jackie Copleton
Ai-ai-gasa: In feudal times, men and women in intimate relations were not supposed to be close together in public, to say nothing of linking arms or holding hands. One of the rare occasions this was permissible was a rainy day when they could enjoy intimacy by sharing an umbrella. Therefore, if a man offered one to a woman, it was often interpreted as an implicit expression of his love for her. Since then a man and a woman in love have been described as sharing an umbrella.