"Stop!"
Alephee commanded and the metal shards turned red. Eren stopped channeling the technique as soon as he heard the voice.
Yet, the flow of the mana couldn't be stopped immediately. So it kept moving for a bit. And this was the reason behind Eren's incoming suffering.
The metal shards were still reacting to the flow of mana inside the mana pathways. They tore his skin and lodged themselves inside it before moving with the flow, making him bleed all over. In a few seconds, Eren's Adept-ranked body was severely injured.
Eren was about to yell in pain. But tonight he held on. There was some part of his mind that was not processing the pain he felt. That part made him proud of himself for not crying. It indicated that he was getting used to the pain.
A shoutout to HiBob_WarBob for refining Eren's speech placed at the end of the chapter. ;)