Short answers, pulled from the story.
System Sacom, formally System Sacom Sales Corp., is a Japanese company based in Tokyo that currently sells electronic devices. It formerly developed video games, first for computers in the 1980s and then for home consoles in the 1990s.
System Sacom had particular success with one series that had a tremendous effect on the sound novel and visual novel genres. The series combined recorded or musical sound with written text.
System Sacom was a member of DOG, short for Disk Original Group, during the period when the Famicom Disk System was popular. Square, known for some of the era's best remembered role-playing games, was one of the group's most prominent members.
System Sacom withdrew from the video game business in 1998, ending roughly two decades of game development.
System Sacom released computer games for platforms including the PC-8801, PC-9801, X1, FM-7, MSX2, MZ-2500, and X68000, then moved to consoles including the Mega Drive, Mega CD, Super Famicom, Saturn, and PlayStation. It also made PC titles for Windows 95.
All of System Sacom's video game intellectual property is currently owned by D4 Enterprise.