This indicates an attack attempt to exploit a Memory Corruption vulnerability in JustSystems Ichitaro Office.
The vulnerability is due to an error when the vulnerable software handles an JYT file. An attacker can exploit this to execute arbitrary code within the context of the logged in user via a crafted JYT file.
Rakuraku Hagaki and Rakuraku Hagaki Select for Ichitaro
System Compromise: Remote attackers can gain control of vulnerable systems.
Refer to the vendor's advisory for updates: