What does Nukemaru do in CK3?

Prowess +2, Prestige +0.2/month, Heavy Infantry Damage +10% (patch 1.20.0.3).

How do you get Nukemaru with the console?

effect create_artifact_nukemaru_sword_effect = { OWNER = root } — runs the scripted effect that makes it, for the character you play (debug mode).

Personal artifact · Weapon

Nukemaru

Masterwork

Nukemaru is a masterwork weapon artifact in Crusader Kings III: Prowess +2, Prestige +0.2/month, Heavy Infantry Damage +10%. Quality 30 and wealth 30; maximum durability 75, and it does not wear out. At game start it goes to the holder of Kanmu Family (starts from 1178.1.1). Patch 1.20.0.3, from game/common/scripted_effects/01_exp1_historical_artifacts_creation_effect.txt.

Quick answers (2)

What does Nukemaru do in CK3?: Prowess +2, Prestige +0.2/month, Heavy Infantry Damage +10% (patch 1.20.0.3).
How do you get Nukemaru with the console?: effect create_artifact_nukemaru_sword_effect = { OWNER = root } — runs the scripted effect that makes it, for the character you play (debug mode).

Said to have been given to a hunter in Ise by Amaterasu herself, this sword was purchased by Taira Tadamori, and is said to have unsheathed itself when a snake threatened his sleep.

Effects

History and who has it

Made before recorded history.
At game start: the holder of Kanmu Family (starts from 1178.1.1).

How it is made

The game creates it with the scripted effect create_artifact_nukemaru_sword_effect. In the console (how to open it), this gives it to the character you play:

effect create_artifact_nukemaru_sword_effect = { OWNER = root }

Built from the effect's file; not run in the game by us.

Source: game/common/scripted_effects/01_exp1_historical_artifacts_creation_effect.txt, common/modifiers (nukemaru_sword_modifier) and the English localisation, Crusader Kings III 1.20.0.3.