Generally speaking, every single line (excluding reserved trains) in the greater Kanto area can be accessed with a single Suica/Pasmo card.
There are exceptions, which fall into three categories:
- Suica accepted until a specific boundary, e.g. Suica is not accepted past Namie (Jōban Line), Kuroiso (Tōhoku Line), Minakami (Jōetsu Line), Matsumoto (Chūō Line). Usually paper tickets are required past these locations but as a tourist it is highly unlikely that you will end up in one of these situations.
- IC card area boundary changes, so trips must tap out and then back in at the boundary station, e.g. Atami (Tōkaidō Line), Kōzu (Gotemba Line). This is a common faux pax even for locals visiting a new area for the first time, since JR East and JR Central routinely run trains across the territorial border on the Tōkaidō and Gotemba Lines, as does Odakyu's Romancecar service.
- Small private railway or rural local line that doesn't take IC cards at all or has a custom ticketing option, e.g. Yukarigaoka Line, Choshi Electric Railway, Kominato and Isumi Railway Lines, Ryutetsu. In these cases you will typically tap out first and be greeted with a cash only ticket machine to proceed further, or station staff who can help you purchase a ticket.
Pasmo publishes a map at https://www.pasmo.co.jp/visitors/en/area/pdf/all.pdf that shows the full network where you can ride on a single journey. For the webpage linking to this map, see https://www.pasmo.co.jp/visitors/en/area/ (in case the PDF link ceases to work).
Fujikyu and the Chūō Line deep into Nagano Prefecture support Suica, Pasmo, and any of the other interoperable IC cards, so in your particular case you should be fine. I am not sure if Fujikyu requires that you tap in/out when transferring at Ōtsuki but instructions at the station should be clear.