Yes, Miona also centered both under and senbatsu but hers is opposite of Asuka's. Miona came from centering senbatsu song and then get dropped to under after few singles. From my point of view, they show Nanase in trailer is to contain about graduates and objectively Nanase is the biggest graduates name. While the portion of Asuka is kind of understandable since because they tried to push her to be more known by the general public. Yet it's just the first trailer, maybe they will contain more story on 2nd trailer if they will release it, who knows?