Building up an -hp/+atk 4* Lachesis

I'm really happy to see someone ask a question like this. Lachesis has been my main healer even before the 2.0 staff update and she has not disappointed. I know tier lists and rankings and stuff like that do not favour her very much, however that only matters if you choose to believe those things.

Her attack stat is quite impressive and with a boon and atk+3 on both A slot and sacred seal, plus a staff of at least 10mt, she can reach 50+ attack. I choose to use her default Absorb+ though which only has 7mt so mines not quite there yet. Her speed isn't very high but I've found that it doesn't have to be, especially with Absorb+ as she can recover some of the damage if shes going to take a second hit.

Quick Riposte 2 or 3 can help with this, and since you said you don't have a Genny, that opens up your B slot for this skill. Of course, you'd want to refine whatever weapon you decide on with the Wrathful upgrade as opposed to the Dazzling one to make the most of her attack.

Her HP is decent so if you're serious about her I'd recommend you get one with a bane in spd or def if you can later on, as her resistance is also pretty good. The assist is up to you, Recover+ sounds good or you can use Physic+ for the extra range.

Overall, she's one of my best units and definitely my best colorless, and she can be both a really strong healer and hard hitter. Here's mine if you wanted to see it.

Hope this helps :)