TAK-360 for Idiopathic Hypersomnia

Key Inclusion Criteria: 1. The participant weighs greater than or equal to (≥) 40 kilograms (kg) and has a body mass index (BMI) between 16 and 38 kilograms per meter square (kg/m\^2) \[inclusive\]. 2. The participant has a documented, current diagnosis of IH. Key Exclusion Criteria: 1. The participant has a current medical disorder associated with excessive daytime sleepiness (EDS) \[other than IH\]. 2. The participant has medically significant thyroid disease. 3. The participant has a history of cancer in the past 5 years. (This exclusion does not apply to participants with carcinoma in situ \[such as basal cell carcinoma\] that has been treated and is stable, or who have been stable without further treatment. These participants may be included after approval by the medical monitor.) 4. The participant has any of the following viral infections based on a positive test result: Hepatitis B surface antigen (at screening), hepatitis C virus antibody (at screening), human immunodeficiency virus (HIV) antibody/antigen (at screening). 5. The participant has a clinically significant history of head injury or head trauma. 6. The participant has history of epilepsy, seizure, or convulsion (exception for a single febrile seizure in childhood). 7. The participant has a history of cerebral ischemia, transient ischemic attack (less than \[\<\]5 years from screening), intracranial aneurysm, or arteriovenous malformation.