Efficacy and Safety of Oral Once-Daily Vonoprazan (TAK-438) in Participants With Erosive Esophagitis

Inclusion Criteria: 1. In the opinion of the investigator, the participant is capable of understanding and complying with protocol requirements. 2. The participant or, when applicable, the participant's legally acceptable representative signs and dates a written, informed consent form and any required privacy authorization prior to the initiation of any study procedures. 3. Has been confirmed in an endoscopy to have erosive esophagitis, ie, the Los Angeles (LA) classification grades A to D within 7 days of the start of the Day 1 (Visit 2). Note: The recruitment goal is to ensure that those with LA classification grade C/D will account for more than 30% of all participants enrolled (144/480), with no further recruitment of those with grade A/B considered when they account for more than 70% (336/480) of all participants. 4. Is aged 18 years old or older (or the local age of consent if that is older), male or female, at the time of signing an informed consent, and is being treated on an outpatient basis for erosive esophagitis, including those admitted temporarily for examination. 5. A female participant of childbearing potential who is sexually active with a nonsterilized male partner agrees to use routinely adequate contraception from signing of informed consent throughout the duration of the study. Exclusion Criteria: 1. Has received any investigational compound within 84 days prior to the start of the Observation phase. 2. Has received TAK-438 in a previous clinical study or as a therapeutic agent. 3. Is an immediate family member, study site employee, or is in a dependant relationship with a study site employee who is involved in conduct of this study (eg, spouse, parent, child, sibling) or may consent under duress. 4. Has, in the judgment of the investigator, clinically significant abnormal hematological parameters of hemoglobin, hematocrit, or erythrocytes at Screening. 5. Has a history or clinical manifestations of serious central nerve system (CNS), cardiovascular, pulmonary, hepatic, renal, metabolic, gastrointestinal, urological, endocrine or hematological disease. 6. Has a history of hypersensitivity or allergies to TAK-438 (including its excipients\*) or to proton pump inhibitors (PPIs). \*D-mannitol, crystalline cellulose, hydroxypropyl cellulose, fumaric acid, croscarmellose sodium, magnesium stearate, hypromellose, macrogol 6000, titanium oxide, yellow iron sesquioxide and iron sesquioxide. 7. Has a history of drug abuse (defined as any illicit drug use) or a history of alcohol abuse within 1 year prior to the Observation Phase (Visit 1). 8. Is required to take excluded medications. 9. If female, the participant is pregnant or lactating or intending to become pregnant before, during, or within 1 month after participating in this study; or intending to donate ova during such time period. 10. Has participated in another clinical study within the past 30 days from Visit 1. 11. Has co-morbidities that could affect the esophagus (eosinophilic esophagitis, esophageal varices, scleroderma, viral or fungal infection, esophageal strictures), a history of radiotherapy or cryotherapy for the esophagus; those with corrosive or physiochemical injury (with the possible inclusion in the study of those with Schatzki's ring or Barrett's esophagus). 12. Has a history of surgical procedures that may affect the esophagus (eg, fundoplication and mechanical dilatation for esophageal strictures excluding Schatzki's ring) or a history of gastric or duodenal surgery excluding endoscopic removal of benign polyps. 13. Developed acute upper gastrointestinal bleeding, gastric ulcer (a mucosal defect with white coating) or duodenal ulcer (a mucosal defect with white coating), within 30 days before the start of the Observation Phase (Visit 1) (with the possible inclusion of those with gastric or duodenal erosion). 14. Has Zollinger-Ellison syndrome or gastric acid hypersecretion or a history of gastric acid hypersecretion. 15. Is scheduled for surgery that requires hospitalization or requires surgical treatment during his/her participation in the study. 16. Has a history of malignancy or was treated for malignancy within 5 years before the start of the Observation Phase (Visit 1) (the participant may be included in the study if he/she has cured cutaneous basal cell carcinoma or cervical carcinoma in situ). 17. Has acquired immunodeficiency syndrome (AIDS) or hepatitis, including hepatitis virus carriers: hepatitis B surface antigen (HBsAg) positive, or hepatitis C virus (HCV)-antibody-positive (the participant may be included in the study if he/she is HCV-antigen or HCV-ribonucleic acid \[RNA\]-negative). 18. Laboratory tests performed at the start of the Early Observation Phase (visit 1) revealed any of the following abnormalities in the participant: 1. Creatinine levels: \>2 mg/dL (\>177 μmol/L). 2. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST), or total bilirubin levels: \> upper limit of normal (ULN). 19. Is active in the Screening Period after the closure of enrollment identified by the Sponsor or the number of participants randomized with LA classification A/B or C/D have reached the required sample size.