Saisen Coin Offering (お賽銭 - Osaisen)
The voluntary monetary offering tossed into the wooden collection box (Saisenbako) at Shinto shrines or Buddhist temples to show gratitude and sincerity. The 5-yen coin is considered the luckiest offering due to a linguistic wordplay.
Ancient Japanese offered freshly harvested rice or fish to express gratitude to nature. As currency spread in the Muromachi period, physical crops were replaced with coins, which developed into modern Saisen offerings.
Do not throw the coin aggressively. Stand close and slide or drop it gently into the wooden box. While any amount is acceptable, a 5-yen coin is highly recommended because '5 yen' (go-en) sounds exactly like 'good fortune/connection' in Japanese.
Which coin is considered the luckiest for Saisen offerings due to sounding like 'good connection'?