|Now that Weapon Refinery is available—and Beruka’s native Killer weapon can easily be upgraded then refined for a relatively affordable 70 Summoning Stones (20 + 50)—even casual Beruka users have nearly no excuse to augment her awesome physical defense even further with a Defense-refined All-purpose. Without taking into account further stat increases from the A-skill slot, Sacred Seal, AND Fortify/Ward boosts, a +0 Beruka with a Defense boon and a Defense-refined Slaying Axe+ sits at a beefy 51 HP and stellar 44 Defense. As usual, '"`UNIQ--item-233--QINU`"' and '"`UNIQ--item-236--QINU`"' procs will be hellishly powerful and only become stronger with new skills, enabling Beruka to essentially ignore her otherwise-terrible Attack while tearing down nearly any unit that can’t off her in time.
Translation: when given all the trimmings, Beruka becomes inhumanly difficult to take down for physical attackers in enemy phase. Obviously, steer clear of magic and ranged units, and don’t overdo it against sword units with high Attack on initiation or defense-decreasing specials, such as Siegbert, Elincia, and Black Knight.
Now, let’s go over said trimmings. '"`UNIQ--item-239--QINU`"' is still the best A-slot passive skill for its value: it can be acquired easily than other passives from any 4-star Seth and gives Beruka a substantial and consistent 5 Def increase. Its Attack penalty does not matter in the grand scheme of things, as Beruka still sports a quite-low Attack even without it. Beruka can also go for more luxurious passives if you are willing to give them; '"`UNIQ--item-242--QINU`"' in particular provides the best Arena optimization due to its higher SP cost and +1 Def over Fortress Def 3. Additionally, Close Def also counts towards Dragonstone damage, making matches against Fae and Nowi significantly more favorable despite Beruka’s below-average Resistance. Mentions of honor include '"`UNIQ--item-245--QINU`"' (budget) and '"`UNIQ--item-248--QINU`"' (less valuable than Close Def but can still be used if lacking that).
Optimal (or '"`UNIQ--item-254--QINU`"' for those on a budget) guarantees a counterattack for Beruka when at high HP, which is significant as she will need that extra attack to successfully kill most baited units with her chosen special. The combination of Quick Riposte, a defensive A-skill, and Beruka’s special is already potent in itself and requires little tweaking. '"`UNIQ--item-257--QINU`"', however, is also worth consideration, as it enables Beruka to confidently go toe-to-toe with attackers without fear of their own special (especially Luna) activating and ruining an otherwise nice matchup.
Beruka’s C-skill slot is flexible and depends on team composition. For flier teams, '"`UNIQ--item-260--QINU`"' or '"`UNIQ--item-263--QINU`"' are very good for offensive support, especially considering Beruka will almost never initiate offensively herself. For more general teams, '"`UNIQ--item-266--QINU`"' or any Hone/Fortify skill are also worth considering. If running Panic Ploy in the C slot is too restricting, you can use its Sacred Seal version. However, Beruka can benefit more from IVs, because despite all her physical bulk, she is still extremely vulnerable to archers. Taking this seal allows her to negate that weakness and utilize her bulk to tank archers who might otherwise defeat her.
As far as boons are concerned, a Defense boon is obvious. Due to Beruka's incorrigibly low Speed, it can be safely lowered for the bane. Although a Resistance bane is tempting due to Beruka's also low Resistance stat, it makes compromises her actually decent matchups against Nowi and Fae.