[schroth-sensei]

The city buses should all be accessible, sightseeing buses often are not (although the Red-Line, Green-Line, and Blue-Line buses are called sightseeing buses, they are also regular accessible city buses). If you don’t have an issue riding in accessible buses where you’re from, you probably won’t have issues here (personally, the rides around the area were very smooth, definitely better than any I’ve had States-side).
All you need to do is make sure when you’re at a bus stop to sit in a vary obvious location so the bus driver see you on arrival (this may be near the front of a bus, but that’s not where you’ll enter). Usually first they will offload any passengers that are disembarking at that location, then speak with you/your caregiver about where you’re going (it is good to have ready a written down location name or it visible on your phone). Then before allowing others on they typically load wheelchairs after placed a ramp, you’ll load using the door in the middle of the bus (as seen in the attached picture of a green-line bus to Lake Saiko). Once you’re settled in, your caregiver can handle paying the fare when they load everyone else in the front, in my case we used Pasmo IC cards, my caregiver touched both our cards to the ic touch pad when boarding and again when exiting to pay.