People with dementia often live with several long-term conditions (known as multimorbidity). These conditions interact with dementia in complex ways and influence symptoms, care needs, and quality of life. Current researches are primarily divided into quantitative or qualitative methods without complementing each other. Most data driven research usually counts diagnoses or groups diseases. Qualitative evidence shows the need, and how daily routines, family roles, and personal goals affect care. These methods do not explain how people manage other long-term conditions alongside dementia. As a result, research findings do not always support care that centres on what matters to individuals. This paper proposes a shift in research on multimorbidity in people with dementia. Unlike other conditions, dementia is often diagnosed in later stage of life, with high burden of multimorbidity. We argue that data base research should focus on symptoms, function, treatment workload, and social context, which could shape how people live with dementia and multimorbidity. It can also inform the transitions between home, hospital, community services, and long-term care. These insights can guide the design of interventions that fit real situations. For evidence generation on symptom-based measures, functional assessments, and patient-reported outcomes, mixed methods studies can show how context, mechanisms, and outcomes interact. We offer a research agenda that places the person at the centre and what works for the patient going beyond the simple disease burden. This agenda supports the development of care that is feasible, acceptable, and meaningful. Without this shift, multimorbidity research may not improve everyday dementia care.