Torii (the gate) of burial mounds are categorized as shinmei torii, which comprise two posts or pillars connected by a shimenawa (rope). They are not associated with any one religion, and are only used for the burial mounds of the members of the imperial family.
Furuichi Kofungun is a part of Mozu-Furuichi Kofungun*, a group of burial mounds in the Furuichi-Fujiidera area. It comprises 130 burial mounds (95 of which are in Fujiidera City) built between 1,450 and 1,650 years ago. 45 of them (29 in Fujiidera) still keep their original mound-shapes, and 26 (17 in Fujiidera) are included in the group that is to be registered as a UNESCO World Heritage site.
There’s no fixed manner for visiting burial mounds, but you can’t go wrong with straightening your clothes and taking off your hat and sunglasses. Bow once at the gate.