Today i am going to give you a little info on Double Yagura opening.Yagura is a Static Rook opening and a castle as well.Usually when one player utilizes the Yagura,so does the second,but this is not "mandatory",as we can also see 4th-File Rook vs Yagura or even 3rd-File Rook Left Mino vs Yagura,Gangi vs Yagura etc.Though building a Yagura castle is considered best fro both sides since it gives interesting and beautiful games,while having a solid castle.It is not a surprise that in the shogi database https://shogidb2.com/strategies Yagura is first in use as a battle pattern/plan so this indicates its importance and value to be used by both sente and gote.
In case of a Double Yagura this is the main formation that arises with whichever move order possible(New Yagura,Old Yagura): (Gote to move)
In Double Yagura both sides try to attack the central pawn of the 3 that are part of the Yagura Castle by firstly moving the knight to 3g for Sente and 7c for Gote and then pushing 4f,4e for Sente and 6d,6e for Gote.Also,another vulnerable point of the Yagura is the edge pawn of the castle which both players try to undermine,sometimes even with bishop sacrifices,moving or dropping the Knight on the e-row and forking the pawn and the silver,or even by utilizing strategies like Spearing The Sparrow,which means moving the Lance forward and then supporting it by moving the Rook on the edge behind it.
In a Double Yagura formation you have to remember that Sente is bound to attack while Gote is bound to defend,since due to the symmetry sente has the initiative.
Below i put some links in case you want to find more info:
http://mangafox.me/manga/81_diver/v13/c135/1.html (It says a little about Double Yagura)
https://www.youtube.com/watch?v=hdcMTPItiew(An analysis of a Double Yagura game between Satoshi and Habu)
https://en.wikipedia.org/wiki/Yagura#/media/File:Funai_Castle_02.jpg (The structure that Yagura Castle was based on)