Study of TAK-935 as an Adjunctive Therapy in Participants With Developmental and/or Epileptic Encephalopathies

Inclusion Criteria

• Has a documented clinical diagnosis of developmental and/or epileptic encephalopathies with countable bilateral motor seizures, defined as an average of greater than or equal to (>=) 2 per month during the past 3 months, based on the investigator's assessment, and a monthly average of >=1 per month during the Baseline Period, based on the seizure diary record.
• Has been taking 1 to 4 antiepileptic drug (AEDs) at a stable dose for >=4 weeks before Screening and the participant or participant's legally acceptable representative is willing to keep the regimen(s) stable throughout the study.
• Has an average of >=1 bilateral motor seizure per month during the 4-week Baseline Period (that is., drop seizures, tonic-clonic, tonic, bilateral clonic, atonic, myoclonic-atonic, myoclonic-tonic-clonic, focal seizures with bilateral hyperkinetic motor features).
• Must agree to not post any participant's personal medical data related to the study or information related to the study on any web site or social media site (example, Facebook, Twitter) until the study has been completed.
• For participants with G-tube/PEG tube, G-tubes/PEG tubes should have been placed and been functioning for at least 3 months prior to screening. Naso-gastric tubes are not allowed.

Exclusion Criteria

• Has received TAK-935 in a previous clinical study or as a therapeutic agent.
• Was admitted to a medical facility for treatment of status epilepticus requiring mechanical respiration within 3 months before Screening.
• Had a vagal nerve stimulator implanted within 6 months before Screening and settings have been changed within 1 month of the Screening Visit and/or anticipated to change during the study.
• Is on ketogenic diet that has been started within 6 months of the Screening Visit, has been changed within 1 month of the Screening Visit, or is anticipated to change during the study.
• Has degenerative eye disease.
• Has a history of suicidal behavior or any suicidal ideation of type 4 or 5 on the Columbia-Suicide Severity Rating Scale (C-SSRS) at Screening. If the participant is unable to comply with the C-SSRS due to developmental status, a parent proxy may be used for the completion of the C-SSRS. The Investigator may also use clinical judgment, which must then be documented in the source document.
• Positive for human immunodeficiency virus, hepatitis B, or hepatitis C infections. (Note that participants who have been vaccinated against hepatitis B [hepatitis B surface antibody (Ab)-positive] who are negative for other markers of prior hepatitis B infection [example, negative for hepatitis B core Ab] are eligible. Also note that participants who are positive for hepatitis C Ab are eligible as long as they have a negative hepatitis C viral load by quantitative polymerase chain reaction [qPCR]).
• Has an abnormal and clinically significant ECG at Screening in the opinion of the investigator, for example, second or third degree heart block or a corrected QT interval (QTc) greater than (>) 450 millisecond (msec). Entry of any participant with an abnormal but not clinically significant ECG must be approved and documented by signature by the principal investigator or appropriately qualified delegate.
• Has abnormal clinical laboratory test results at Screening that suggest a clinically significant underlying disease. If the participant has alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST) >2.5*the upper limit of normal (ULN), the Medical Monitor should be consulted.
• Has received any excluded medications, procedures, or treatments during the time periods.
• Has any a history of alcohol, opioid, or other drug use disorder, as per the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, within the previous 2 years before Screening. Medical marijuana use is allowed.
• Has unstable, clinically significant neurologic (other than the disease being studied), psychiatric, cardiovascula