Research ethics are crucial for ensuring responsible research activities, and ethical review processes are effective in identifying potential issues prior to conducting experiments. Ethical reviews typically assess data acquisition, processing, management, and the adequacy of informed consent based on established guidelines. However, their primary function has been to monitor and constrain research activities, focusing on the prevention of ethical violations. While stringent ethical reviews in healthcare research emphasizing safety are widely understood, ethical considerations are also essential in service design research. This paper reframes research ethics as a proactive and collaborative means to foster co-creative relationships with participants. We present a case study from an online rehabilitation service design project involving elderly, vulnerable participants and propose a participant-centered framework for research ethics. Concrete examples of measures in the project demonstrate the necessity of revising ethical guidelines to incorporate practical and effective techniques. We analyze this framework from the perspectives of rapport-building and participant motivation.