Inclusion Criteria:
Healthy Participants:
1. Aged 20-55 years, inclusive, at the time of informed consent and first study medication dose.
2. Is a healthy adult male or female of Japanese descent (born to Japanese parents and grandparents and has lived outside of Japan for less than 5 years).
3. Weighs at least 45 kg and has a body mass index (BMI) between 18.0 and 28.0 kg/m\^2, inclusive, at Screening.
Participants with Stable Schizophrenia:
1. Is aged 18 to 55 years, inclusive, at the time of informed consent and first study medication dose.
2. Is an adult male or female with a diagnosis of schizophrenia or schizoaffective disorder.
3. Weighs at least 45 kg and has a BMI between 18.0 and 35.0 kg/m\^2, inclusive at Screening.
4. Has been receiving a stable dose of antipsychotic monotherapy for at least 1 month prior to Screening.
5. Has not had an acute exacerbation of psychosis or been hospitalization for the treatment of schizophrenia or schizoaffective disorder for at least 3 months prior to Screening.
Exclusion Criteria:
All Participants:
1. Has uncontrolled, clinically significant neurologic, cardiovascular, pulmonary, hepatic, renal, metabolic, gastrointestinal, or endocrine disease or other abnormality (other than the disease being studied), which may impact the ability of the participant to participate or potentially confound the study results.
2. If female, the participant is pregnant or lactating or intending to become pregnant, or intending to donate ova, before, during the course of the study or within 12 weeks after last dose.
3. Intends to donate sperm during the course of this study or for 12 weeks after last dose.
4. Has evidence of current cardiovascular, central nervous system, hepatic, hematopoietic disease, renal dysfunction, metabolic or endocrine dysfunction, serious allergy, asthma hypoxemia, hypertension, seizures, or allergic skin rash. There is any finding in the participant's medical history, physical examination, or safety laboratory tests giving reasonable suspicion of a disease that would contraindicate taking TAK-063, or a similar drug in the same class, or that might interfere with the conduct of the study. This includes, but is not limited to, peptic ulcer disease, seizure disorders, and cardiac arrhythmias.
Healthy Participants:
1. Has a history or treatment of Axis I/II mental disorders according to Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) such as depression, anxiety disorders, bipolar disorder, attention deficit hyperactivity disorder (ADHD), autism spectrum disorders, anorexia nervosa, bulimia nervosa or schizophrenia within the past 3 years.
2. Has used nicotine-containing products (including but not limited to cigarettes, pipes, cigars, chewing tobacco, nicotine patch or nicotine gum) within 28 days prior to Check-in Day -1. Cotinine test is positive at Screening or Check-in (Day -1).
Participants with Stable Schizophrenia:
1. Has a history of a primary DSM-IV axis I diagnosis other than schizophrenia or schizoaffective disorder.
2. Has not discontinued antipsychotic or other psychotropic medications or is unable to discontinue antipsychotic or other psychotropic medications at Day -7 (or five half-lives prior to Day -1).
3. Is taking a concomitant medication for a medical condition at a stable dose or regimen for less than two months or is taking a concomitant medication for a medical condition for less than two months and for which the discontinuation for the study period is not medically permissible.
