Isidro has always dreamed to be, if not a soldier, the best mercenary warrior of his time. The inspiration for his ambitions is the legend of a once formidable captain - the great "Hundred Man Slayer" - who fought in the original Band of the Falcon. Although Guts has never revealed to Isidro that he is in fact the young boy's idol, he has supported his dream nonetheless. Being a younger member of the group, Isidro looks up to Guts as a father figure, despite his insistence to the contrary. Currently, he is training under Guts, hoping to achieve his dream of becoming the greatest swordsman in the world.
Rather than teaching Isidro his moves, Guts instructs him to learn to fight using his own style, as each person has a different strength, speed, height, and arm-reach. Isidro develops his spinning move using a cutlass, passed down to him by Morgan, and the Salamander Dagger, given by Flora.
While fighting against the pirates, Mule Wolflame accuses Isidro of not taking the fight seriously as he does not use any moves with the potential to seriously injure or kill an opponent. Isidro's relationship with Schierke, who considers him to have the appearance and intellect of a monkey, is also considerably strained. However, the apparently cynical Isidro is shown to care, at times, for the young witch. In fact Sonia, upon hearing Schierke talking about her bond with Guts and witnessing Isidro fight Bonebeard for her sake, asks gleefully if the swordsman Schierke is attracted to is Isidro himself.
Even considering his character flaws, Guts has demonstrated some degree of faith in Isidro's qualities, encouraging him to find a style suited to him more than Gambino did for the swordsman himself in the past. Despite refusing to label him as such, Guts has found in Isidro an apprentice to whom he always has words of wisdom and encouragement.
When receiving compliments individually or as part of the group Isidro and Puck normally brag about how they can manage things themselves. However, both vastly exaggerate their own aptitude for combat. The two are extremely close friends and Puck often sits on the young boy's head, seeing himself as a mentor of such to the boy. Puck attempts to teach him in the ways of the "Elf Dimension Style", to little success.
Although he and Schierke often get into arguments, he cares for her and for women in general. He is shown defending Isma when she appears to be a mermaid, and when Isma has no place to go he lightheartedly asks Roderick to let her stay with the Seahorse's crew. However, he also becomes easily flustered around women as well, particularly when their breasts are exposed, as seen when he rescues a naked Nina from the assault of pagans at Albion. Isidro also finds Casca attractive, and tries to spy on her while she bathes, but is stopped by Schierke.
Conviction Arc Edit
In a small village that has been abandoned in light of the disasters befalling Midland, Isidro is confronted by several bandits who desire the food he has collected. The young boy allows them to take his earnings, but tricks them into eating only the tainted food, keeping the edible portion under his vest. He dispatches one of the now poisoned bandits with sausage links and proclaims his name to the enemy. When the rest of the bandits appear, Isidro feigns tears while claiming Kushan soldiers suddenly attacked and injured their allies. Before the bandit group can see through Isidro's lie, however, they are killed by Kushan scouts, Isidro only surviving thanks to the presence of Guts. In awe of Guts after witnessing him dispatch the entire scout force with ease, too astonished to speak, Isidro follows after him.
Isidro eventually reaches Guts as he sleeps against a tree stump at dusk, attempting to pick up the swordsman's Dragon Slayer as a test of his strength while being encouraged by Puck to do so. The commotion causes Guts to awaken and he tries to tell the boy to leave him alone; the boy lacks too much experience to follow a branded man like him. However, they are soon attacked by breaking wheel bound corpses, Isidro horrified at the sight. After Isidro's blade breaks during the fight, Guts flings the boy away to safety while leading his undead pursuers away.
Millennium Falcon Arc Edit
Fantasia Arc Edit
In his travels alongside Guts, Isidro learns to use his small stature and natural agility to his advantage. With his natural battle intuition and the few lessons received from Guts, Isidro develops into a competent warrior, capable of killing several trolls and holding his own against experienced older opponents such as Mule and Bonebeard. He uses his surroundings to his advantage and Guts trusts in his skills to fight along side him. Isidro is able to spar with Azan and briefly give him trouble, though is defeated soon after.
- Salamander Dagger: Bestowed onto him by the great witch Flora, the Salamander Dagger is magically crafted from molten lava and imbued with the power of fire elementals. It is hot enough to melt steel and strong enough to combust a human-sized enemy whenever it strikes a successful blow. It is also used to ignite the miniature bombs given to him by Guts.
- Cutlass: Passed down from Morgan's father, who won it in a bet with a sailor, to Morgan and then to Isidro, the cutlass is small enough for Isidro to wield quickly and pierce enemy flesh.
- Miniature Bombs: These small explosives are gifted to Isidro by Guts. They are used in conjunction with the Salamander Dagger for quick ignition.
- "Isidro" is the Spanish variant of the Greek name "Isidore", which means "gift of [the goddess] Isis". Ishidoro is a combination of two Japanese words: "ishi" (stone) and "dorobō" (thief).
- Isidro was modeled after a child of an assistant who worked with Kentarou Miura at the time of the Conviction Arc's publication, and is considered by Miura to be like a child of the Shōwa period.
- In episode 1 of the 2016 anime, Isidro is introduced at a bar in Koka, where he attempts to convince a group of bandits to let him join them so that he can learn how to fight. After he berates the bandit group's leader for wasting his time, he is attacked in retaliation and nearly killed before Guts enters and saves his life. An impressed Isidro attempts to follow after the swordsman, only to lose track of him during a heavy rainstorm.
- Isidro is the only person Guts has been shown to train.
- ^ Berserk, Volume 18, "Spirit Road (1)"
- ^ a b Berserk, Volume 19, "Black Swordsman on the Holy Ground"
- ^ Berserk, Volume 28, "Garrison"
- ^ a b c d Berserk Official Guidebook
- ^ Berserk, Volume 18, "Kushan Scouts (1)"
- ^ Berserk, Volume 29, "A Meager Supper"
- ^ Berserk, Volume 29, "Warrior"
- ^ Berserk, Volume 36, "Quaking Heart"
- ^ Berserk, Volume 24, "Elementals"
- ^ Berserk, Volume 25, "Qliphoth"
- ^ Berserk, Volume 26, "Retribution"