Hm... let's look at the synergy of each presented option in the context of options you've already purchased.
You have ++INT, ++++CHA, +Might, ++++AGI, Might's Repose, Fell-Handed Stroke and Rank 4. You acquired the Evening Sky.
Relative to your overall advancement, your Might is rather low, your Agi and Cha are high, and your Int is quite high. Your Rank would be impressive if you weren't currently exhausted and you have three vectors of esoteric attack (Ring of Power, Power of Ruin, Fell-Handed Stroke). Aside from Rank, your greatest overall assets are your comprehensive defenses and high Charisma, and it was precisely the latter that allowed you to bait the superior combatant Seralize into an overextension.
Let's Break Down the Might Point we have right now into it's equivalent Strength and Constitution pluses, translating our stats into
++INT, ++++CHA, +Strength, +Constitution, ++++AGI
Fall of Night Gives us two strength points, an agility point, souped up and cheaper blade projections, combined with trapdoor insurance, which comes in handy given we're about to dungeon crawl.
++INT, ++++CHA, +++Strength, +Constitution, +++++AGI
The Stat boosts for Undying Vanguard take this to ridiculous heights while protecting our companions
++INT, ++++CHA, ++++Strength, +++++Constitution, ++++++AGI
Now round this out with an Echo of the Forebear(+Might, +Agility AKA +Strength, +Constitution, +Agility)
++INT, ++++CHA, +++++Might, +Constitution, +++++++AGI
Or Converted into Strength+Constitution, this is...
++INT, ++++CHA, +++++Strength, ++++++Constitution, +++++++AGI
[X] Forebear's Blade - Echo of the Forebear
[x] Forebear's Blade - Fall of Night - 2 Arete
[x] Forebear's Blade - Undying Vanguard - 7 Arete
[X] Letrizia - Hollow Star
Basically, we're a Lightning Tank with this.