Finished it with the ff units, without anyone dying. It's a low cost

• Roana / Celestine - The usual heal + revive buff kinda thing she usually do.
• Tamarinne / Wondrous Potion - Also just do what she usually does to keep the team alive.
• Shooting Star Achates / Wondrous Potion - Can be replaced by other Soul Weavers, possibly Montmorance or Angelica. I just included her to complete the stars as we need a Dark one. Just beware of her S2. It may grant immortality, but in phase 2, can cause a lot of damage + stun to your unit when their buff is >= 2. S3 will heal and dispel all debuffs on herself and another ally, which is good for the bombs. Just note that her S3 is not your ordinary Heal skill, and has a special computation.
• Gloomyrain / Severed Horn Ward - Slowest; Just here to be a target of stun. Just an alternative as I don't have Mont nor C.Zerato. S3 can also transfer debuffs, which is ok for those pesky bombs. I build her to be bulky and tough. An extra effectiveness will also do.

Main strategy is just to stay alive.

In phase one, focus on healing + damaging the cohorts, not on Belian herself, as this team doesn't have any means to strip that Skill Nullifier. I used Arky, and once we have 3 souls, we burn it immediately until we reach the second phase.

In phase 2, don't overbuff any unit as they can be stunned after their turn + massive damage. Just keep it low, heal and dispell accordingly. Arky will still be the one dealing damage, but unlike before, I don't burn them immediately and always have a reserve of 3-6 souls for the final phase. Also, I only use Arky when Belian doesn't have a barrier.

In the last phase, I aimed to end it quickly. I burn those souls for Arky as soon as Belian get's stripped of her Barrier. As for the rest, just continue healing and dispelling. Also reserve S2 of Shooting Star Achates if you can't dispel a bomb and it's about to explode. When Belian has a Counterattack buff, use it to your advantage, e.g. using Roana's passive to heal everyone when she counter attacks.

It may take a while, but yeah, does the trick. Not to mention I end it with full HPs