L'Arc Berg Sickle/Relationships

Naofumi Iwatani
L'Arc and his comrade were tasked to killing the four Holy Heroes of the other world, especially the Shield Hero, whom Glass considered as a threat. L'Arc heard about Naofumi from Glass, and also other rumors of the Shield Hero from Melromarc commoners, completely believing such rumors. He even encountered a number of fake heroes and got fed up in his search.

When he came face to face with Naofumi, he was too friendly with him and refused to believe him to be the Shield Hero, as he claimed to be. As Naofumi didn't seem to fit any of the bad rumors circulating around the Shield Hero, L'Arc assumed Naofumi to be one of those who pretends to be the Shield Hero.

After confirming that Naofumi was indeed the Shield Hero, he tried to kill him in a fair fight. He was thrilled to fight Naofumi and enjoyed the resourcefulness of the Shield Hero. He refuses to believe all the rumors of Naofumi's "evil deeds" and claims that there must be a reason for his doings.

When they meet again in the Spirit Tortoise, which was under control of Kyo Ethnina - whom they both saw as an enemy, they entered a temporary alliance. When Naofumi enters L'Arc's world and ends up befriending Kizuna, they eventually rekindle the old relationship they had before L'Arc tried to kill him. This bond eventually developed into a deep and true friendship after they finally defeated Kyo, where they're willing to trust each other in battle. After seeing L'Arc's home and influence, it inspired Naofumi to create his own territory to fight the Waves. Since their first meeting, L'Arc calls him 'Kiddo' to a point where he finds it uncomfortable to call him by his real name while Naofumi, after visiting L'Arc's homeworld, calls him 'Boy'.

Motoyasu Kitamura, Ren Amaki and Itsuki Kawasumi
L'Arc heard so many rumors about him but never seen them. In an extra chapter of the LN, L'Arc and the gang went to the hot spring in the Cal Mira Archipelago, where Motoyasu proposed to peek into the separated women's bath to which L'Arc called them to be his comrades and joined them.

He didn't believe them to be the heroes as they claimed to be and thinks that they are one of those who pretends to be a hero like the fake shield heroes. He easily knocks them out with a single slash and worried that he might kill them if he uses a little more force.

Therese Alexanderite
They are close and always got into scuffles from time to time. Therese doesn't restrain herself from using physical force against L'arc in case of disagreement

It was well known that L'arc has romantic feelings for Therese. But her views of L'arc was not mentioned. As noted by Glass, L'arc progress is pathetic. (In an extra chapter of Light Novel), Nafoumi assumed L'arc and Therese to be a couple but was proved otherwise, by L'arc action of desperately trying to peek her in the bathhouse.