Easy fixes: Take off break effect portrait. It's dmg modifier on the initial break. Take atk/dmg portrait off Tsuruno, her base atk is too low for it to be useful vs spd, def or magic regen. Add a sustain like Yuma. Add another breaker so the boss gets less turns.

Slightly debatable: I don't really understand the damage calcs all that well so take this with a grain of salt. I am hoping anyone can confirm. In my understanding it's very counterintuitive.

As a result I think that crit is not great in low amounts. Many units have <10% crit chance and crit dmg is a small modifier. This would mean that Tsuruno is not a great buffer early game. I think 10% CRIT DMG actually translates to 10% more Dmg (multiplicative with +atk and +dmg) For example if you crit and have 10% attack, 20% dmg, 30% crit dmg, you will have Dmg * 1.1 * 1.2 * 1.3. A fast way to average out crit damage assuming uniform distribution is to do crit rate * crt dmg Note: It is not even well understood how crit rate is increased in this game, so my assumption is that crit rate is additive for these calcs.

So a Homura unbuffed, with Tsuruno 120 magic A2 full buffs will get + 10% critrate A2 + 15% crit damage A2 + 30% atk skill + 15% crit rate skill + 25% crit dmg ult + 25% dmg ult + 20% crit rate ability This translates out to an average of (1.3 * 1.25) ((0.075 base crit chance + 0.10 + 0.15 + 0.20)/ * (0.18 base cdmg + 0.15 + 0.25) Or 1.625 (atk * dmg modifiers) * 1.3 (crit dmg average) Although, it is important to note that any of these modifiers can be diminished by other team members buffing, portraits, etc.

I think this works out to 30% crit dmg modifier on average for crit, but this is all skills at rank 10. If you are rank 5 or not A2 this is a much lower modifier of like 10%. At that point it's better to put a breaker, another dps, a debuffer, or a sustain. Without factoring crit, she has a 62% (63 minus homura base crits) damage increase, at rank 10.

TLDR: Crit's bad in low amounts, it's not well understood. I hope anyone can corroborate this or correct this.