I think the lack of character development in M0 (there is a little, mostly with Shin and probably with Sara coming soon) can be attributed to the fact that the time frame of the series is quite short. M+'s time span went for 3 months. M7's timespan went for more than a year, infact, almost 3. M0's time span? Well...I'd give it about a month of work. The way the episodes are strung together, there is no time lapse. The next episode picks up right where the last one left off. There's no gap. And you know the old saying, you can't expect someone to change overnight.