18th Divisiion was ‘square’, with 23rd and 35th Brigades. In the process of triangularizing the 18th, the 23rd Brigade HQ became 18th Div Infantry Group HQ and the 35th Brigade HQ was split out, along with 124th Inf Rgt, under command of MGen Yamaguchi Kiyotake and designated the ‘Kawaguchi Detachment’ (remember Kawaguchi?).
This unit has a long participatory history in the early stages of the war, both in Borneo and in the Solomons. Because of organizational provenance (and command evolution), it is identified by many names: 35th Brigade (although it wasn’t a brigade); 124th Inf Rgt (although it had attachments over the Regimental level); Kawaguchi Detachment (probably the most descriptive, until Kawaguchi gets whacked); Oka detachment (124th Inf Rgt, as long as Kawaguchi wasn’t around); and various other names of Bn commanders after the unit organization dissolved under combat stress on Guadalcanal.
As Terminus so aptly describes, welcome to the wonderful world of Japanese unit designations.