[GS] Tenebrius 7* Solo (ft. Raphtalia and Gerald)

In this run, we will take on Tenebrius, a raid boss with powerful attacks and several unique passives which
1) render taunt tanks useless since the boss removes all shields and inflicts heavy damage when under 50% HP, and
2) render traditional healers useless since the boss applies a massive healing debuff.
Recommended units include Vox and Swick for their good team-wide Max HP up buffs (which circumvent the healing debuff), as well as consistent art gen units such as Fen and Mako to keep the party going and cycling through abilities.
But what if... you lack those units?
Are taunt tanks really just dead weight here?
In this run, we'll take down the strongest raid boss with Raphtalia, Millenia, Berwick, and Gerald, taking advantage of several unique mechanics:
1) The synergy of Raphtalia and Millenia's Arts to create a near infinite source of pseudo-heals for the tank
2) The extreme effectiveness of Berwick's arts as an art gen, especially for fire units (and also because I literally don't have any other art gen units due to bad decision making)
3) The unique passives of several pieces of equipment and Gerald himself, giving the tank an extremely high amount of innate damage mitigation.
This is by no means the perfect comp or the fastest strategy, but for someone aiming for the top of the leaderboard with none of the recommended units, this was the only option.