Common for Phase 2a Part and Phase 2b/3 PartAnd commmon for mild/moderate and asumptomatic SARS-CoV-2-infected participants- Participants with a percutaneous oxygen saturation (SpO2) during wakefulness of =< 93% (room air)- Participants strongly suspected to have pneumonia- Participants who need oxygen administration- Participants who need a mechanical ventilation - Participants who are strongly suspected to have worsening of symptoms of SARS-CoV-2 infection within 48 hours after randomization, in the opinion of the investigator/subinvestigator- Participants with suspected active and systemic infections requiring treatment at the time of randomization (excluding SARS-CoV-2)- Current or chronic history of moderate or severe liver disease or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)- Current or chronic history of moderate or severe kidney disease- Participants who have used any of the following drugs within 7 days prior to randomization(approved/unapproved drugs for the treatment of SARS-CoV-2 infection, antiviral, antibacterial, or antifungal drugs [excluding topical use])- Participants who have used any of the following drugs within 14 days prior to randomization(strong CYP 3A inhibitor, strong CYP 3A inducer, products containing St. John's wort)

Common for Phase 2a Part and Phase 2b/3 PartAnd commmon for mild/moderate and asumptomatic SARS-CoV-2-infected participants- Participants with a percutaneous oxygen saturation (SpO2) during wakefulness of =< 93% (room air)- Participants strongly suspected to have pneumonia- Participants who need oxygen administration- Participants who need a mechanical ventilation - Participants who are strongly suspected to have worsening of symptoms of SARS-CoV-2 infection within 48 hours after randomization, in the opinion of the investigator/subinvestigator- Participants with suspected active and systemic infections requiring treatment at the time of randomization (excluding SARS-CoV-2)- Current or chronic history of moderate or severe liver disease or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)- Current or chronic history of moderate or severe kidney disease- Participants who have used any of the following drugs within 7 days prior to randomization(approved/unapproved drugs for the treatment of SARS-CoV-2 infection, antiviral, antibacterial, or antifungal drugs [excluding topical use])- Participants who have used any of the following drugs within 14 days prior to randomization(strong CYP 3A inhibitor, strong CYP 3A inducer, products containing St. John's wort)

Common for Phase 2a Part and Phase 2b/3 PartAnd commmon for mild/moderate and asumptomatic SARS-CoV-2-infected participants- Participants with a percutaneous oxygen saturation (SpO2) during wakefulness of =< 93% (room air)- Participants strongly suspected to have pneumonia- Participants who need oxygen administration- Participants who need a mechanical ventilation - Participants who are strongly suspected to have worsening of symptoms of SARS CoV 2 infection within 48 hours after enrollment, in the opinion of the investigator/subinvestigator- Participants with suspected active and systemic infections requiring treatment at the time of enrollment (excluding SARS CoV-2)- Current or chronic history of moderate or severe liver disease or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)- Current or chronic history of moderate or severe kidney disease- Participants who have used any of the following drugs within 7 days prior to enrollment(approved/unapproved drugs for the treatment of SARS-CoV-2 infection, antiviral, antibacterial, or antifungal drugs [excluding topical use])- Participants who have used any of the following drugs within 14 days prior to enrollment(strong CYP 3A inhibitor, strong CYP 3A inducer, products containing St. John's wort)

Common for Phase 2a Part and Phase 2b/3 PartAnd commmon for mild/moderate and asumptomatic SARS-CoV-2-infected participants- Participants with a percutaneous oxygen saturation (SpO2) during wakefulness of =< 93% (room air)- Participants strongly suspected to have pneumonia- Participants who need oxygen administration- Participants who need a mechanical ventilation - Participants who are strongly suspected to have worsening of symptoms of SARS CoV 2 infection within 48 hours after enrollment, in the opinion of the investigator/subinvestigator- Participants with suspected active and systemic infections requiring treatment at the time of enrollment (excluding SARS CoV-2)- Current or chronic history of moderate or severe liver disease or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)- Current or chronic history of moderate or severe kidney disease- Participants who have used any of the following drugs within 7 days prior to enrollment(approved/unapproved drugs for the treatment of SARS-CoV-2 infection, antiviral, antibacterial, or antifungal drugs [excluding topical use])- Participants who have used any of the following drugs within 14 days prior to enrollment(strong CYP 3A inhibitor, strong CYP 3A inducer, products containing St. John's wort)

Common for Phase 2a Part and Phase 2b/3 PartAnd commmon for mild and asumptomatic SARS-CoV-2-infected participants- Participants with a percutaneous oxygen saturation (SpO2) during wakefulness of < 96% (room air)- Participants strongly suspected to have pneumonia- Participants who need oxygen administration- Participants who need a mechanical ventilation - Participants who are strongly suspected to have worsening of symptoms of SARS CoV 2 infection within 48 hours after enrollment, in the opinion of the investigator/subinvestigator- Participants with suspected active and systemic infections requiring treatment at the time of enrollment (excluding SARS CoV-2)- Current or chronic history of moderate or severe liver disease or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)- Current or chronic history of moderate or severe kidney disease- Participants who have used any of the following drugs within 7 days prior to enrollment(approved/unapproved drugs for the treatment of SARS-CoV-2 infection, antiviral, antibacterial, or antifungal drugs [excluding topical use])- Participants who have used any of the following drugs within 14 days prior to enrollment(strong CYP 3A inhibitor, strong CYP 3A inducer, products containing St. John's wort)

Common for Phase 2a Part and Phase 2b/3 PartAnd commmon for mild and asumptomatic SARS-CoV-2-infected participants- Participants with a percutaneous oxygen saturation (SpO2) during wakefulness of < 96% (room air)- Participants strongly suspected to have pneumonia- Participants who need oxygen administration- Participants who need a mechanical ventilation - Participants who are strongly suspected to have worsening of symptoms of SARS CoV 2 infection within 48 hours after enrollment, in the opinion of the investigator/subinvestigator- Participants with suspected active and systemic infections requiring treatment at the time of enrollment (excluding SARS CoV-2)- Current or chronic history of moderate or severe liver disease or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)- Current or chronic history of moderate or severe kidney disease- Participants who have used any of the following drugs within 7 days prior to enrollment(approved/unapproved drugs for the treatment of SARS-CoV-2 infection, antiviral, antibacterial, or antifungal drugs [excluding topical use])- Participants who have used any of the following drugs within 14 days prior to enrollment(strong CYP 3A inhibitor, strong CYP 3A inducer, products containing St. John's wort)