What are the rules for swimming and holding your breath?

Question

Where do I find rules for swimming/holding breath in L5R 4e?

I am preparing to start a game set in the Mantis lands, and one of my players is considering playing an Order of Togashi monk. When we started talking about tattoos, I announced that anything that wasn't defined could be created and my player asked for a tattoo that made it so the character could breathe underwater. To create a fair mechanic, as well as prepare for when a more mundane character ends up in the water, I would like to know if there is a RAW for swimming/holding breath/drowning.

I am preparing to invent something involving Stamina + Athletics (Swimming), but for now all I can find are the rules for going without food/water or sleep.

Answer 1

The closest I think you will find to rules on swimming are on p.83 of the core book under drowning.

You must make a TN 15 Athletics(swimming)/Strength check every minute to stay afloat. TN increases with difficult conditions (like stormy waters or wearing heavy armour) and increases further based on how long you have been in the water. failure means you sunk underwater and can potentially start drowning.

Strictly speaking these rules are for treading water, but I think they can easily apply to swimming. Set a TN based on the desired distance traveled if a roll per minute is too much hassle and apply bonuses or penalties based on conditions like swimming against the current, allow raises to be used to improve speed, swim underwater etc.

Answer 2

L5R Core rules for 4th edition have, on page 139:

ATHLETICS (STRENGTH)

SUB-TYPES: None

EMPHASES: Climbing, Running, Swimming, Throwing

... Athletics covers many areas normally governed by Trait Rolls. If you have a background in Athletics, however, you can perform these activities, principally climbing, running, and swimming, with considerably more ease than most. ...

So as a basis, swimming is an athletics skill. For staying above water, the rules are on p.83, indicating a TN 15 keeps you at the surface under normal circumstances (e.g. dressed, no rough sea). For prolonged stays in the water, the roll goes on Stamina for threading water. It also tells that if you fail the roll, the character goes under and...

can hold his breath for a number of Rounds equal to his Stamina. [...] If he is still underwater when his Stamina runs out, he begins drowning, taking 2k2 Wounds per Round.

So holding breath is automatic.