Marcel Galliard

Marcel (マルセル) was a comrade and childhood friend of Reiner Braun, Bertolt Hoover, and Annie Leonhart. He was part of the group sent by the Hometown to attack humanity in year 845, but his mission was frustrated by the sudden appearance of Ymir in her mindless Titan form.

Clash of the Titans arc
When a group of Titans are attacking a tower in Utgard Castle, Reiner leads the other rookies in defending the interior of the tower. He attempts to barricade the door against an invading Titan, and recalls being attacked and nearly killed by a Titan many years earlier. Before the Titan could catch him, he was pushed out of the way by Marcel and was forced to watch the Titan devour his friend in his place. He is snapped out of the memory by Bertolt calling for him. The two manage to fend off the Titan and promise to return to their hometown together.

The following morning, with no weapons and their superiors all dead, the rookies prepare for the end. However, Ymir reveals her secret and transforms into a Titan, fighting to save the others. Reiner and Bertolt were shocked when they realized that Ymir is the same Titan that attacked them years earlier and is responsible for killing Marcel.

Later, in a forest, Bertolt expresses concern over whether they can trust Ymir and reminds Reiner of Marcel's death at her hands. He later questions Ymir about it, and she states that she does not remember doing it. Bertolt accepts her apology, and states that she probably did not want to eat anyone.

After they escape to the Shiganshina District, Ymir expresses her gratitude towards Reiner and Bertolt for their role in freeing her from her Titan form. She agrees to return to their hometown with them, even though doing so could very well mean her death. As an explanation, she mentions her desire to repay them for what she took; possibly referring to Marcel's death at her hands.

Eren Yeager later recalls the conversation between Bertolt and Ymir, and writes it down immediately. The information is given to Hange Zoë, who rushes away to share it with Commander Erwin Smith. Hange reveals this information threatens their current plans, as it reveals Titans can absorb the powers of victims they devour. In this way, the powers of a devoured Titan Shifter such as Marcel transfers to the Titan that devoured them. Hange theorizes the same process could be used to transfer the Coordinate from Eren to a preferred host, which is later proven when Rod tries to get Historia to eat Eren in this fashion.

Trivia

 * In the original version of Chapter 47 and in Crunchyroll's digital manga service, he was addressed by the name "Berwick" (ベリック). However, in Volume 12, his name was changed to "Marcel".
 * His name, Marcel, is French in origin, meaning "Little Warrior". Considering the group he belonged to refer to themselves as "Warriors", it is no coincidence.
 * His original name, Berwick, is English in origin, meaning "Grain Farm". This contrasts with his companions' names and incidentally represent the three basic levels of society—Rulers/Land Owners (Bertolt), Soldiers/Warriors (Reiner), and Farmers (Berwick).

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Berwick