@boag
Murata adds things, but ONE must approve it first. ONE has full control over story.
From a 2015 Interview:
http://opmcityz.blogspot.com/2016/04/onemurata-2015-joint-interview.html
Murata: For the main storyline, the dialogue stays pretty much the same. But with side-stories, sometimes I’ll try adding in scenes to ONE-sensei’s storyboards, or change the dialogue up a bit. In such cases, I’ll always ask ONE-sensei’s opinion. We’ll go back and forth fine-tuning it…and sometimes it’ll just end up reverting back to how it was in the beginning (laughs).
ONE: Murata-sensei always shows me whenever he thinks up new scenes or dialogue to add. For instance, with the A-Class hero Spring Mustachio, my storyboards just had his name and general appearance. He talked a bit and got beat up by the monster, nothing more. I didn’t plan to highlight what weapons he used or anything like that; that part was really cut short. But the storyboards Murata-sensei came up with featured him using his weapon against the monster, showing off his fighting chops so that the monster looked even more impressive by comparison. It was fantastic!