Butanuki is a recurring savings tool following the Dollar Cost Averaging model. DCA involves investing the same amount of money at regular intervals regardless of the state of the market.
Over the long term, this strategy makes it possible to "smooth out" volatility and thus reduce risk, while maximizing the amounts invested, since it follows the market curve.
In addition, it is an excellent tool for planning ahead the budget allocated to the investment, without being influenced by emotions. The budget remains fixed each month or week, according to your own means (the golden rule: only invest what you don't need in the short term, and can afford to lose!)
This method applies perfectly to Bitcoin, since the saver buys fractions of BTC (called "satoshis").