A Study of TAK-105 in Healthy Adults

The drug being tested in this study is called TAK-105. The study will look at the safety, tolerability, and PK of TAK-105-a and TAK-105-b in healthy participants. Participants in each cohort will be randomized to receive treatment with TAK-105-a or TAK-105-b or matching placebo which will remain undisclosed to the participant and study doctor during the study (unless there is an urgent medical need). The study consists of 6 parts and up to 34 cohorts as mentioned below: * Part 1 (SRD) will enroll healthy participants in up to 12 cohorts. * Part 2 (MRD) will enroll healthy participants in up to 5 ascending cohorts. * Part 3 (Dose titration) will enroll healthy participants in up to 6 multiple-dose cohorts. * Part 4 (Redosing) will enroll healthy participants in up to 4 redosing cohorts. * Part 5a (SRD) will enroll healthy Japanese participants in up to 3 cohorts. * Part 5b (MRD) (optional) will enroll healthy Japanese participants in up to 2 cohorts. The MRD cohorts in Part 5b will be optional, depending on the PK and safety data observed in Part 2 (MRD). * Part 6 (SRD) will enroll healthy participants in up to 2 cohorts. Each cohort in all the parts will have 8 randomized participants with 6 participants receiving a single dose of TAK-105-a in Parts 1 to 5 or TAK-105-b in Part 6, and 2 receiving TAK-105-a matching placebo (Parts 1 to 5) or TAK-105-b matching placebo (Part 6) in a 3:1 ratio. This multi-center trial will be conducted in the United States. The overall duration of the study is approximately 18 months.