Sword Without End was in hell to protect Jiaye from any mishaps, for if Jiaye ran into trouble in hell, he wouldn't be able to resurrect, meaning permanent death.
This was Chen Yi's greatest worry.
The reason he liked Jiaye and could still bring himself to attack him was largely because he knew that even if one fell into hell, they could still come back up, and it wasn't a true death.
But if one were to die again in hell, there would really be no future at all.
Therefore, he was always concerned about Jiaye encountering any trouble in hell, with some sightless thing annoying or provoking him, which is why he always asked Sword Without End to accompany him. With Sword Without End's strength, he couldn't exactly strut around in hell,
but protecting Jiaye from harm was absolutely no problem.
It might seem like Sword Without End wasn't very strong in their team, everyone could rebuke him a couple of times, and he had an exceptionally good temper, appearing to be an old softie.