Read on Twitter
Mugino’s death and the potential meaning behind was really beautiful man so just a quick thread on what I feel the writers were trying to portray with it
So first we got the foreshadowing of his death which is linked with a turtle given to him by the old lady in the scene she mentions how the shadow of death follows a close friend (I believe this is a reference to Team 7 as a whole or Konohamaru)
In Japan a turtle symbolises a number of things such as protection, longevity, luck, etc but one of the interesting ones is uniting heaven and the earth with the shell representing heaven and it’s underside representing the earth
In his death Mugino activates a jutsu which collapses in the top of the cave. I feel as though this was meant to symbolise his passing on to heaven with the top of the cave representing the shell (heaven) and Mugino’s jutsu representing the underside (Earth) to unite the two
The reminder he gave for Boruto especially is why it’s got me feeling this way since it’s in direct reference to the turtle as well as the divine light shining over the rubble, could be a reach but if intended it’s a very nice and subtle detail added in by the anime
Given the life Mugino lived and his wanting to atone the sins the world forced upon him as a child I think him giving his life to save Kono and the rest of the team the same way the man he attempted to assassinate did in his lifetime is also beautiful a fitting end for him
Also wanted to add that the turtle also symbolising luck and protection could have also been the reason Orochimaru was conveniently timed to save Mugino and Konohamaru as well as Mitsuki saving Boruto and Sarada in their fight too
Hopefully there’s more added scenes to show Boruto acknowledging the turtle and maybe even using it in future scenes to remind him how Mugino affected his life even for the short time they spent together in missions 
