Rush.
Select an enemy follower on the field and engage it.
If it's your turn, look at the top 5 cards of your deck. You may summon up to two 1-cost Aqua Force followers from among them. Put the rest on the bottom of your deck in any order.
QIf I summon 2 copies of Tear Knight, Theo onto an empty field with Storm Rider, Diamantes's Last Words ability, do I give both copies Rush and Assail?
AYes. Since both copies of Tear Knight, Theo are summoned simultaneously, there's "another Aqua Force follower on your field" when each of their Fanfare abilities triggers.
QIf this follower is destroyed during my end phase, do I still look at the top 5 cards of my deck and summon up to two 1-cost Aqua Force followers from among them?
AYes. Your end phase is still part of your turn.