Aoba Shrine sits in a quiet wooded area near the old castle grounds and is dedicated to the deified spirit of Date Masamune. The shrine was established in the Meiji period and has a restrained, dignified character — less ornate than Osaki Hachimangu but with a genuinely serene atmosphere, especially on weekday mornings when it's nearly empty.
The shrine is a short walk from the castle ruins, making it easy to combine the two. The grounds are pleasant to wander, and the main hall has good examples of Shinto architectural detail. Omamori (protective charms) here often feature Date Masamune's iconic crescent-moon helmet and are popular with visitors. The annual festival in late July draws local participants and is worth catching if you're in the city.