Pre-Cathedral Michiru would have chosen solitude over anything else, surrounded by music or books; she would have chosen to travel the world and tour as a famous violinist, and would have absolutely given up being a Senshi because I think part of her really hated how much destruction and death she couldnāt prevent.
And she wouldnāt ever let herself think about a family, or Haruka, because she didnātĀ ādeserveā that sort of happiness, and she didnāt want to impose on other people.
(Before the altercation at the Marine Cathedral, Michiru had a lot of issues. She still does, but sheās more honest about them.)
Post-Cathedral Michiru - post-death Michiru, post-resurrection/post-watching-Haruka-die-as-well-Michiru just - chucks all those thoughts of doubt and self-hatred and what she does and doesnātĀ ādeserveā straight out the metaphorical window.Ā
And I think after that her idea of perfect happiness is still quiet, still includes music and traveling, but itās expanded to encompass her family. I think Michiru is blindingly, ecstatically happy when sheās spending quiet conversations with Setsuna, or playing with Hotaru, and of course - doing pretty much anything with Haruka. And this includes the other Senshi too. I think Sailor Moon - and the other inner Senshi - helped her realize that she doesnāt need to be ruthless and cold to be a good soldier. She doesnāt need to sacrifice her humanity.
So I think being around her friends and family in quiet, normal moments - thatās Michiruās idea of perfect happiness.