There's a book review that briefly mentions these as:
the case of the Japanese suicide bomb-infantrymen at Port Arthur during the 1904 – 1905 war with Russia.
A Reddit answer claims no such stuff happened though. (There are some quotes in that thread from some books on the 1904-1905 war, but while these mention ruinous frontal assaults, they don't mention any suicide bombing in that war.) So, what's the extent of knowledge on these? I can't seem to find much else about them.