Starting from the assumption that Japanese has no subject–verb agreement, this paper focuses on the acquisition of agreement, specifically on structure building of a functional category AGRP (agreement phrase) which provides a configuration in which nominative case is licensed/checked in a bi-unique SpecAGR relation. L2 clausal structures corresponding to Japanese multiple subject sentences receive particular scrutiny since the possibility of licensing more than one subject phrase is expected to influence L2 implementation of an AGRP in this context. Relying on a written corpus, the paper outlines a transition to a grammar with AGR, drawing on lexical learning (Clahsen, Eisenbeiss and Penke 1996), structure-building (Vainikka and Young-Scholten 1996, 1998) and elements of constructionism (Herschensohn 2000). The data indicate that Japanese speakers create a bi-unique spec-head relation for agreement. However, in clauses corresponding to multiple subject sentences, instances of failed agreement suggest that co-indexing is not yet consistently carried out with the phrase in SpecAGR. Also, instances of inappropriate predication and caseless DPs indicate that creation of AGRP does not bring about an immediate solution to the problem of integrating the multiple subject phrases in Japanese into English clausal structure.