Yes it does have a side airbag in the seats and you cannot put a seat cover over that. The seat cover would have to have a proper installation so that it does not interfere with the airbag.
Has for the seats, the Micra SR seats are great! A lot better than in the Micra S. The dealer told me they cost 1200$ each, so that would be an expensive switch.
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View my fuel log 2015 Micra SR automatic: 7.0 L/100 km ... 40.4 mpg (Imp) ... 14.3 km/L ... 33.6 mpg (US) ...