With the same understanding as Lynn, it is possible to report those related lines using the following method... buckle up!
Create your report using the BKARHIVL table. Create a parameter field (PartNumber) to prompt for the part number you are reporting on, or create a formula field (PartNumber) and store it there.
Create a running total field (Related) that summarizes BKAR_INVL_INVNM by type "count", evaluate using a formula as such...
Code:{BKARHIVL_B.BKAR_INVL_PCODE} = {?PartNumber}
...and reset using a formula as such...
Code:{BKARHIVL_B.BKAR_INVL_PCODE} <> "" and {BKARHIVL_B.BKAR_INVL_PCODE} <> {?PartNumber}
Create a formula field (Related) containing something like...
Code:if {#Related} > 0 then "R"
Then, to have the report show only those lines that are "related," you must format your details section to suppress those lines where...
Code:{@Related} <> "R"
...and there you go!
Field names and other parts of this solution are suggested and subject to change according to your configuration and/or style, but should give you a general idea of how to accomplish the task. HTH! 8)