First off: I have no association with the projects: Danganronpa and Danganronpa Rebirth Voices; this is fanmade.
During this chapter, Marin kills Seshi Yodogawa
Last chapter, Seshi was revealed to be some kind or assassin. The group tied hi. up and Marin accidently kills him(most of the other students attempt to kill Seshi).
The text "ミズタさんがクロに決まりました。"
vaguely translates to "Mizuta san has been selected as the blackened"