Kato has a Very Long lifespan
Ninja Kato, being of that sexy rare breed, lives even longer
If you are using the same monsters, however, I might reccomend:
- Avoiding Battles as much as possible (go for the highest reward ones only after going through all the grades)
- Keep your monster well rested (pretty obvious imo)
- Maintain Even nature (use Smoked Snake if it gets Soft or worse, Apple Cake for the opposite)
- Maintain Normal form (Candy to fatten it up, Powder to make it thinner)
- Avoid Errantries for at least the first couple of years (I loved the moves of this guy so I went for a lot of the POW moves)
- Keep it's stress level low (mint leaves)
Nuts Oil is also handy for fitting in extra training