Saizo vs. Saizo (The Family Name of Saizou in the Japanese version) is Paralogue 9 of Fire Emblem Fates.
This paralogue is unlocked once Saizo has achieved an S-Support with any female character.
The script for this paralogue can be found here.
Utilizing the Dragon Vein on this map will cause the walls to collapse.
Subjective: The following part of this article is based upon the editor's personal experiences and opinions, and therefore may not be applicable for all readers.
Unlike other chapters, the objective in this chapter is to defeat (or capture) Funke before Asugi escapes the map. Players will need a Royal unit aside of Corrin (who joins in automatically) to make progress on the map, as the Dragon Vein is a very important factor to beat this paralogue. It will destroy a section of the wall, allowing your units to take drastic shortcuts to reach Funke; if you do not wish to break the walls, bring a unit with Locktouch so they can open the doors for you. However, this will take much longer than using the Dragon's Vein, so this is not recommended.
Asugi starts just east of your starting position in a locked room, using his Locktouch to open the doors in his path and attempt to escape. There are three doors blocking his path in a zig-zag formation, so he will take a while to escape due to being an unpromoted unit. As he is an allied unit, this is even further complicated because of the presence of two units right outside the last door.
Funke is able to move normally, so once he is within reach of your units, lure him towards you. It's best to dispatch or capture him immediately, as any further moves can result in Asugi being killed by the enemy outside the third door. However, if you feel confident, you may send some units to deal with said enemies to the third door area and then keep Funke immobilized (by having four units surrounding him, or three that keep him against a Wall tile) until all the other ruffians are dealt with, while also blocking the passage in the north so Asugi will not use it to escape.
Once Funke is killed/captured, the paralogue ends immediately.