Acute ischemic stroke (AIS) is a medical emergency that happens because of a sudden stop of blood flow to a part of the brain. This happens when a blood clot forms within the vessel (known as thrombotic occlusion) or a clot originating from somewhere else blocks a blood vessel (known as embolic occlusion). Strokes can cause serious health problems, death, and affect one's quality of life. To reduce long-term damage, it is important to restore blood flow to the brain as soon as possible.

The main aim of this study is to check how safe TAK-755 is, and how well adults with AIS tolerate it. Other aims are to check how well TAK-755 helps participants to manage their everyday activities and to understand whether it helps reduce the seriousness of their stroke symptoms when compared to placebo. A placebo looks like TAK-755, but does not have any medicine in it, to make sure participants do not know which treatment they are taking.

The participants will receive TAK-755 or placebo once; afterwards, their health will be monitored for about 3 months (90 days). All participants, regardless of their assignment to either TAK-755 or placebo, will receive the usual treatment for AIS as per the hospital's normal practice.

Inclusion Criteria:

Informed Consent:

1. The participant or legally authorized representative has provided informed consent before the initiation of any trial procedures.

   Age:

2. 18 to 80 years of age, inclusive, at the time of signing the informed consent form.

   Clinical Characteristics:

3. Clinical diagnosis of AIS.

4. Onset of stroke symptoms within 24 hours of enrollment. Wake-up strokes may be included if Last Known Well is within 24 hours of enrollment; time of onset will be considered the time of Last Known Well.

5. National Institutes of Health Stroke Scale score of 6 to 25, indicating moderate to severe stroke.

6. Estimated Modified Rankin Scale score less than (<) 2 prior to AIS presentation, signifying no significant disability.

7. Signs and symptoms consistent with anterior circulation stroke.

   Imaging:

8. Evidence of causative AIS occlusion on imaging (intracranial internal carotid artery [ICA], M1, M2, M3, M4, A1, A2, A3).

9. Evidence of salvageable brain tissue on CT or MR imaging.

Exclusion Criteria:

Medical History:

1. Weight >130 kilograms (kg) or <40 kg.

2. History of severe traumatic brain injury in the past 90 days.

3. History of intracranial hemorrhage.

4. History of intracranial neoplasm except for small meningioma.

5. History of prior stroke in the past 90 days.

6. History of intracranial or intraspinal surgery within the past 90 days.

7. Major surgery or severe trauma in the past 14 days.

8. History of cerebral amyloid angiopathy.

9. History of systemic malignancy, except for locally excised basal cell or squamous cell skin carcinoma with clear margins.

10. Diagnosis of serious, advanced, or terminal illness with anticipated life expectancy of less than 1 year.

11. Participation in other interventional clinical trials within the previous 90 days.

12. Known life-threatening hypersensitivity reaction to TAK-755 or its components.

13. Any prior administration of TAK-755.

14. Administration of caplacizumab in the past 30 days.

15. Administration of von Willebrand factor-containing products in the past 14 days.

16. Baseline conditions (prior to the index AIS event) that prevent an understanding of the nature, scope, and possible consequences of the trial, in the judgment of the investigator.

    Current Stroke Management:

17. Any prior administration (intravenous or intra-arterial) of alteplase or tenecteplase for the index AIS event, as well as any prior administration of prourokinase or reteplase for the index AIS event in countries where approved.

18. Eligible for administration of intravenous thrombolysis (alteplase or tenecteplase, as well as prourokinase or reteplase in countries where approved) for the index AIS event, based on the site's standard clinical guidelines and direct availability.

19. Intent to proceed with endovascular thrombectomy (EVT) for the index AIS event based on eligibility and direct availability.

20. Seizure at time of index AIS event onset.

21. Persistent blood pressure elevation (systolic >=185 millimeters of mercury [mmHg] or diastolic >=110 mm Hg) prior to randomization.

22. Blood glucose <50 milligrams per deciliter (mg/dL) or >400 mg/dL.

    Current Medical Conditions:

23. Active, uncontrolled bleeding.

24. Bleeding diathesis or any other conditions that would pose significant bleeding risk.

25. Inability to undergo MRI or CT.

26. Rapidly improving AIS symptoms.

27. Chronic causative intracranial occlusion.

28. Causative total occlusion of the extracranial ICA.

29. Evidence of septic emboli or bacterial endocarditis.

30. Another clinically significant concomitant disease that may pose additional risks for the participant in the opinion of the investigator.

31. Pregnancy, lactation, or unable to comply with birth control methods or abstinence as specified in the protocol in the opinion of the investigator.

    Imaging:

32. Poor quality imaging that precludes interpretation according to trial protocol.

33. Evidence of significant intracranial mass effect or midline shift.

34. Evidence of occlusion in >1 vascular territory.

35. Evidence of acute or chronic intracranial hemorrhage.

36. Evidence of extensive early ischemic change estimated to be greater than one-third of the middle cerebral artery territory.

37. Evidence of intracranial tumor (except incidental, small meningioma), cerebral aneurysm, or arteriovenous malformation.

    Laboratory:

38. Platelet count <50,000/ cubic millimeters (mm^3).

    Other:

39. Identification by the investigator as being potentially unable or unwilling to cooperate with trial procedures.

Takeda provides access to the de-identified individual participant data (IPD) for eligible studies to aid qualified researchers in addressing legitimate scientific objectives (Takeda's data sharing commitment is available on https://clinicaltrials.takeda.com/takedas-commitment?commitment=5). These IPDs will be provided in a secure research environment following approval of a data sharing request, and under the terms of a data sharing agreement.

IPD from eligible studies will be shared with qualified researchers according to the criteria and process described on https://vivli.org/ourmember/takeda/. For approved requests, the researchers will be provided access to anonymized data (to respect patient privacy in line with applicable laws and regulations) and with information necessary to address the research objectives under the terms of a data sharing agreement.