As you can already tell, each time Guts uses the armor is a little bit different. This instance is no exception and part of the incremental development Guts is going through.
What happens in Vritannis is that in order to get to the boat quickly, Guts and his companions are facing a whale familiar again.
Guts is taking this one down without using the Berserker Armor as aid, as he learned their weakness during the incident at the beach. Because we established that he was conscious as he has slain the first familiar like this, he still remembers their weak spot (the breathing hole they have at the top of their heads).
He took this one whale down and then proceeds fighting the Daka crossing their way. Throughout this, once again you see Guts struggling not only with his enemies, but also with himself, trying to hold the Beast of Darkness back.
What’s also noteworthy that every time Guts gets to taste some blood, we see the Beast of Darkness taking its chances to take over.
After the Daka have been slain by Schierke’s fire spell – he encounters five more whale familiars .
Again, Guts realizes he cannot fight THESE things without using the armor. He STILL is weakened. He has slain the tiger familiars and the Dakas before, and before shit hit the fan at Vritannis, he was bed-ridden with fever too.
So he is telling Schierke to get off his back, as Guts – by his own will – plans on using the Berserker Armor. Schierke at this point is exhausted from the fire spell she cast just a couple of minutes before that. She panics as she realizes the Beast of Darkness is materializing on his cape. She refuses to let go, because she knows she cannot help him in this state, fearing what will happen if she lets Guts do this by himself.
This is when Schierke’s spirit is drawn into the armor. She is observing the fight as she resides inside of Guts’ consciousness.
After the whales were slain, another enemy much bigger than the familiars enters the scene: Daiba and his Kundalini, the water snake – the latter being god-like spirit.
When Guts is attacking Daiba recklessly, she decides to bring Guts back. She realizes that this is a type of enemy that cannot be defeated by brute force – but by Guts’ incredible combat wit, that happens to get lost when he’s going berserk like this.
Note how Guts’ pupils fades back in, as Schierke touches his right eye to see. The fact there was no visible pupil before this possibly means that either 1) Guts must have mostly given in to the Beast of Darkness, or 2) that its influence over Guts has increased in strength and thus had already sucked him in. What is also weird is that Flora’s amulet isn’t anywhere to be seen.
Guts stops all his movements in confusion, causing him to fall down. Mid-flight, he decides to use his sword as gliding device to dampen his fall. He eventually lands on the Kushan galleass.
Later using his sword, he stops the mast falling down onto his companions, saving them.
The fact that Miura switches perspective here (from Guts’ perspective to observer perspective) is genius from a writing point of view. It has the reader wondering what happened to Guts to make him do this – killing machines don’t save people.
Now because this is the only instance where Guts was in full control for most of the time, the observations relevant to this article stop here. The only noteworthy event that happens later is how Guts goes back to his full human state: namely that he is being electrocuted by Ganishka.
With Schierke being present during invocation of the Beast of Darkness, Guts gains additional control over it, enabling to stay in control throughout the fight. Schierke is physically present during the invocation and leaves her spirit inside of Guts’ consciousness. What is also noteworthy is that in this instance, it is established that Guts can go back from sane berserker form to his normal self by experiencing shock (in this case: electrical). This will happen again later on.
The next time Guts uses the Berserker Armor is against the Sea God Pirates.