As long as Kosei is enchanted, equipped, and has a counter on it, Kosei has "Whenever Kosei deals combat damage to an opponent, you draw that many cards and Kosei deals that much damage to each other opponent."

Equipped creature has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.) At the beginning of your upkeep, put a +1/+1 counter on equipped creature if it's green. Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)