"Immodithymic character" (Shuuchaku Seikaku), as proposed by Mitsuzo Shimoda in 1929, has been widely accepted as the premorbid personality of manic-depressive illness. However, how he developed the theory of immodithymic character remains unclear. The purpose of this study was to clarify the process used to construct the theory of immodithymic character by comprehensively investigating the literature written by Shimoda and comparing the contents with the theory of psychopathic personalities by Masatake Morita.
 Shimoda originally considered that manic-depressive illness and paranoia develop on the basis of psychopathic personalities, but did not specify the psychopathic types that were associated with each disease. He later came to associate specific psychopathic types with manic-depressive illness and paranoia. On the other hand, he also noted that manic-depressive patients displayed a "simple and honest, timid, and earnest" character.
 Shimoda first proposed "immodithymic character" in 1929, but had already noted the three elements of "simple and honest, timid, and earnest", "quarrelsome", and "excitable" as premorbid characteristics of manic-depressive illness by 1928, in addition to "quarrelsome" and "enthusiastic, fanatical" as premorbid characteristics of paranoia.
 In 1929, Shimoda stopped classifying psychopathic personalities with superficial features, as Kraepelin was doing. He then reclassified psychopathic personalities so as to group some types with the same property into a single category and relate that category to specific diseases with the same nature. The three elements of: 1) "simple and honest, timid, and earnest", 2) "quarrelsome", and 3) "enthusiastic, fanatical" were then grouped into "immodithymic character" under the common property of "lasting affect" (abnormality of the excitability of affect), and immodithymic character was related to manic-depressive illness and paranoia. The taxonomy of grouping psychopathic personalities with the same properties and the approach to setting the common term "lasting affect" are in common with the classification of Morita, who criticized Kraepelin. Given this construction process, the author can conclude that immodithymic character is a complex personality type with three components.
 From the 1930's, Shimoda emphasized the relationship between a depressive episode of manic-depressive illness and immodithymic character, and focused on the element of "simple and honest, timid, and earnest". Immodithymic character excluded the association with paranoia and became a key concept to differentiate manic-depressive illness from neurasthenia. As a result, immodithymic character became similar to "Typus melancholicus" (melancholic type) later proposed by Tellenbach.
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