He has brown hair and blue eyes.
At first he was looking like a young Knight of the Kingdom.
Sigurd was originally a somewhat fragile person, who only had his fiancee, Aina, to keep him mentally in one piece.
On Day 116 (day 121 in the manga) it's shown that when he arrived at his village, most of the villagers were dead, not understanding what happened he went looking for survivors.
Finally finding Aina he ran at her, but at the moment they were about to touch themselves she was cut in two by a centipede monster. Lost in memories he repelled the monster, which most likely left full and satisfied.
The death of his fianciee during the attack resulted in a psychotic break and a beserker state.
Found by Aporou, during his First Expedition, in a village holding the upper half of his lover, he was overcome with rage and fought with Rou. After being easily defeated by him he fainted, leaving Aporou and Dhammi to bury the corpses. Waking up he revealed why the village was in that state.
Aporou proposed to him some devil contract: helping him to exact his revenge in exchange of integrating Parabellum. He was reluctant at first but when Rou told him that he knew who was controlling Arutirumu, he chose to follow him.
Him, named Sigurd Ace Sven from the Sternbild Kingdom left to be replaced by Avenger.
[ Fate Plunder ] activation erased Avenger's Hero Psalm from the Kingdom's National Psalm to be integrated in Rou's World Psalm thus making Rou the one to manage his abilities and control his growth.
He is doing a variety of requests along with Rusty Iron Knight and Scarface. The requests mostly consist of eliminating thief and bandit camps, or subjugating dangerous monsters causing havoc for towns and villages who offer up the quests to remove them.
Day 272 Ovarou took him and his subcasts to train, fighting against some summoned monsters. Each one of them was doing his role but their cooperation was still weak. After some hours of battle under the pouring rain they became real comrades.
Day 291 because of the repeated training sessions, they have really improved their coordination.
Without needing to speak, they communicate with just the slightest glance or movement. They're learning to read each others intentions which in itself is great progress.
They're now managing to cooperate fluidly at high speeds, even though there are still occasional rough patches, they comfortably earn a passing grade.
Initially, his relationship with his group was rather dull since he perceived them as nothing but a tool to increase the rate of success of his revenge. Now that he has fulfilled it, it's unknown if his point of view about them has changed.
He has the God of Sunlight's Divine Protection.
Sigurd was a rather skilled swordsman due to his hero training on the city but his personality made him hard to deal deadly blows. After succumbing to his vengeful thoughts and turning into the Avenger, his senses seem to be sharper and has no doubts on cutting through.
Furthermore, he is a Hero with his own Psalm, which means that he has access to really powerful abilities though, now that his Psalm is controlled by Rou, it's not longer up to him whether or not to trigger those skills.
After the first training he proved himself to be stronger than what Rou thought but still relying too much on his levels and arts.
Since his cast is complete, he is the one fighting in the forefront.
Day 289 Ovarou offered him the special ability [Demonic Insect's Natural Enemy] which he bought in the Holy Land of Gambling's shop. It permits him to deal critical damage to insects.
At first he was wearing the normal equipment of a Knight from the Sternbild Kingdom.
Afterward, Rou let him use his sword: 【Sunlight's Soul Sword, Hisperiol】. Rou was the one keeping it since it was awarded to him after Avenger's defeat when they first met.
By winning in the Colosseum of the Holy Land of Gambling against its champion he gained [Notorious Indestructible Armor] and [Fate of Attracting Cloak]. Starting to look like the [Hero of Sunlight].