Kafka is a nihility character that applies the shock debuff to enemies, acting as a subdps. Each turn, shocked enemies take damage that scales with Kafka's atk. This damage does not crit and depends on atk (as well as dmg bonus, def, res). So one could just build full atk on Kafka.
The Stellaron group Silver Wolf, Blade, Kafka work quite well with each other. Silver Wolf's NA can debuff enemies while proccing Kafka's attack, and Blade's dps is NA focused, which can also proc Kafka's attack.
When a character does a NA, Kafka does a coordinated atk that applies shock on the enemy. This can proc once every X seconds. The effect hit rate can be replaced by a function of the crit rate. Shocked enemies will take tick dmg every 3 seconds that scales with Kafka's atk. The shock debuff lasts for 12 seconds.
Kafka's E does an aoe blast that makes shocked enemies immediately take shock dmg equal to a portion of the tick dmg. Her Q does an aoe attack that applies shock to all hit enemies, while making them immediately take shock dmg equal to a portion of the tick dmg.
In Genshin, the electro-charged reaction (scaling with EM) is a bit similar to the shock debuff in that both do not crit (ignoring Nahida C2). However, the shock debuff does factor dmg bonus and def.
There is already a Genshin character that does electro dot automatically: Yae Miko. The difference between Kafka and Yae is that Yae can crit. Kafka would be able to deal more damage if she could crit on her dot.
But this sort of thing is similar to making Yelan scale with hp and not benefit from Bennett, making kokomi unable to crit, or making Nilou's main source of damage her bloom (EM scaling, not crit). However, at least Kafka can be used in more types of teams than Nilou.
Anyways, as Yae already exists in Genshin, there may be little need to introduce a Kafka type sub-dps in Genshin.