ACT (Vanguard circle) Once per turn: Generation break 2: (Active if you have 2 or more face-up G Units in your vanguard circle or generation zone) [Choose two of your rearguards, and retire them] During this turn, this unit gets Power +10000 / Critical +1.
AUTO (Vanguard circle): [Counterblast 1] During your turn, when your G unit strides, you may pay the cost. If you do, search your deck for one grade 1 or less card, call it to a rearguard circle, shuffle that deck, during this turn, that unit gets Power +2000.
As was predicted, Claret Sword's on-stride counterblast 1 superior calls a grade 1 or lesser card from the deck and temporarily increasing its power, allowing a weaker unit with a utility skill to temporarily serve as a valuable booster before being retired by stride skills. The primary issue working against Claret Sword is the lack of genericized support for Shadow Paladin; the Revengers are the clan itself, and most effective support cards that do not belong to them instead go to the Blasters specifically.
Sovereign Star Dragon units, the card Claret Sword fighters will want to take advantage of the most is Black-winged Swordbreaker from BT15: Infinite Rebirth. Swordbreaker's on-call soulblast 1 to draw will build a net +2 in card advantage if Claret was strode over neutrally, refreshing the hand, providing a temporary base 8000 power booster and providing fuel for retire-based strides. Another potential target is the original Black Sage Charon from BT04: Eclipse of Illusionary Shadows and TD10: Purgatory Revenger, who with the power bonus will become a 10000-power booster that can form 21000-power lines with either Triple Dark Armor or the generation break 12000-power attacker Belberith.
The Dark “Ren Suzugamori” will not be compatible with Claret Sword because these units require a Blaster vanguard, but if your stride target is Phantom Blaster “Diablo” this won't be a problem for that turn. You can use Claret Sword to superior call Darkheart Trumpeter, use Darkheart's soulblast 1 to superior call Pitch Black Sage Charon, and since you have Blaster “Diablo” as your vanguard you'll be able to use Charon's Blaster-exclusive skill to make him count as two units at once, incurring a net change of 0--the same exchange as if you'd called Swordbreaker. The difference between Pitch Black Charon and Swordbreaker is that Charon allows you to maintain field presence, while Swordbreaker maintains handsize. Charon is an offensively-minded play, while Swordbreaker is defensively-minded.
Phantom Blaster Dragon, down to its timing. Everything learned from Blaster Dragon years ago is applicable, including its shortcomings, but lets consider first how Claret improves the skill. Claret Sword does away with the counterblast cost entirely to get rid of the redundant costing on Blaster Dragon, meaning that so long as you have cards you can put into play, you can use his generation break. And only costing two units instead of three helps offset the lack of access to Pitch Black Charon for the Sovereign's retire skill. Phantom Blaster Dragon does have access to the generation break skills of Knights Dorint and Claudas from their legend deck to unflip damage with, and can make use of Darkheart, Swordbreaker and Charon, while on his own independent turns Claret does not have access to either Darkheart or Swordbreaker (the latter by connection to the former.)
Thus Phantom Blaster is generally looking at a counterblast 1 soulblast 1 retire 2 for his skill, sometimes at a net -1 rather than -2, and because Claret Sword has to wait so much later in the game to get his skill online in the first place, it's less immediately available by comparison. The major shortcoming of the Sovereign Dragon's generation break is that there are so many other cards with almost identical skills that are able to make use of them without paying any cost at all; Dragonic Blademaster, Battle Deity Susanoo, Dragonic Vanquisher and Charharlot Vampir all receive similar benefits passively rather than by actively needing to pay a cost. Secondary to this is that like with Phantom Blaster Dragon because Claret Sword's retire skill is a main phase retire that requires fronting two rearguards it has a hidden second cost, that essentially takes four cards out of your defenses. Every two units that you retire in the main phase have to be replaced with two more from the hand, weakening your overall ability to defend. A further discussion of these types of abilities is addressed in the History of Professional Cardfight. Where Claret has a leg up over his predecessor is that across several cumulative turns he is able to amass greater overall card advantage through repeated on-stride superior calls, and this can make him more viable in the long term. It simply weakens his overall offensive gameplay in terms of the generation break, which like Damned Charging Lance before it is destined to go unused.
Finally, Claret Sword's lore;
Shinseikokka no yami ni ikiru kurokikishidan "Shadou Paradin" no kishi.
Chi no you ni akakushimatta sono kenkara "Kuraretto Soodo" no na de yobareru.
"Chikarakoso Seigi" to iu shinnen wo mochi, kishidan ni zokushiteinagara "shinseikokka wo kagekara shieru" to iu shisou ni i wo tonaeru.
Living in the darkness of the holy nation, there is a knight of the black order "Shadow Paladin."
Because of his blade stained red with blood, he is called "Claret Sword."
Believing that "power is justice," he opposes the ideal of "supporting the holy nation from the shadows" in spite of belonging to a knightly order.