The primary purpose of this study is to demonstrate the bioequivalence (BE) of a single subcutaneous (SC) dose of lecanemab via vial and AI in healthy participants.

Inclusion Criteria:

1. Non-smoking, male or female, age greater than or equal to (>=) 18 years and less than or equal to (<=) 65 years at the time of informed consent. To be considered non-smokers, participants must have discontinued smoking for at least 4 weeks before dosing
2. Body Mass Index >=18 and less than (<) 30 kilogram per square meter (kg/m^2) at Screening

Exclusion Criteria:

1. Clinically significant illness that requires medical treatment within 8 weeks of dosing or a clinically significant infection that requires medical treatment within 4 weeks of dosing
2. Evidence of disease that may influence the outcome of the study within 4 weeks before dosing; example, psychiatric disorders and disorders of the gastrointestinal tract, liver, kidney, respiratory system, endocrine system, hematological system, neurological system, or cardiovascular system, or participants who have a congenital abnormality in metabolism
3. Currently enrolled in another clinical study or used any investigational drug or device within 28 days or 5 half-lives of the other investigational drug, whichever is longer, preceding informed consent
4. Prior exposure to lecanemab, or any other anti-amyloid therapies
5. Hypersensitivity to lecanemab or any of the excipients, or to any (monoclonal anti-body [mAb]) treatment

Eisai's data sharing commitment and further information on how to request data can be found on our website http://eisaiclinicaltrials.com/.