You probably never can complete all of the trials in The Anan Fortress. It's true. Nobody can get access to the area with the barrier where I was told to come back when I am stronger. The developer removed access to that area.

Boss in Borghild is like a test dummy made for player to test their skill build using time ability and relic passive ability to reach maximum damage.(this area respawn boss everytime you re-enter even you already defeat it) you can't beat it in the early stage of the game with low level character. I suggest you progess story further, gain all time manipulate ability, level up character and explore look for more relic that hidden in the game (some of them are overpowered if you combine it right) and comeback later. you can see in the video the indicator in the right of the screen show the effect of relic. for example I use a relic that Increase 50% of damage when you make 100 combo hit and when combine with "time resonance" ability that create 3 more shadow its help you multiply attack damage.