This paper examines an agreement suffix called "peripheral agreement" in Delaware (Algonquian) that is able to manifest both differential subject marking (DSM) and differential object marking (DOM) in the same position. In particular, Delaware subjects do not normally show differential agreement marking, but exceptionally, when the subject of a transitive clause is inanimate or obviative, DSM occurs. This paper argues that this limited type of DSM follows exactly the same principles as an analysis rooted in Diesing's (1992) movement-based account to DOM. Specifically, I argue that non-prototypical agents (i.e., inanimate or obviative) originate in Spec-vP while prototypical agents (i.e., animate) originate in Spec-VoiceP (cf. Tollan & Oxford 2018). Consequently, their lower base position allows inanimate and obviative subjects to participate in the same movement-driven differential agreement pattern. This paper shows that a Diesing-style analysis not only correctly captures Algonquian DOM associated with definiteness and DSM related to animacy, obviation, and definiteness, but also provides us a unified treatment of two phenomena with one syntactic account.