I believe the mission of a Sailor Senshi is different for each one. For example, my mission is protect Elysion, Helios and those I love. For me to do this mission, I give up everything to have everything, to protect what I love and to do it with all my heart. Its the only way to do my mission.

However, the mission of the senshi of the shrine is to protect the moon princess (which is myself) and the diamond I hold. They must protect it with their life, and they do it so well.

The senshi of Sailor Moon are to protect Sailor Moon with their life and to ensure that her crystal is protected. The mission of sailor moon is to fight for love and justice and to peserve peace.

The mission is different for everyone, but the one thing that all the senshi missions have in common is thus; protect and defend. The Senshi stand for this the most.