Sidekicks are an important part and selling point of the PC version of Daikatana, but their implementation and performance has been criticized harshly.
The movement of Superfly and Mikiko is dictated through various nodes placed around the map. The AI will try to stick to the nodes for movement.
Since Superfly and Mikiko are two different sidekicks, they use separate nodes to prevent clumping and clipping, but due to Mikiko being implemented later in the game, her node placement is very untested, and she uses much fewer nodes, leading to running into walls and bad movement. This is very evident throughout the game, particularly during ladders.
The AI will rush headfirst into combat - even if they are only equipped with a melee weapon against a powerful foe. This means that finding weapons for the AI and keeping them well stocked with ammo is important - that way they will at least keep a little distance. They don't retreat automatically - so be sure to use the sidekick commands to tell them to back off or move elsewhere from combat.
The AI will take damage from the player - and will use voice responses to notify you to stop, and that they took damage. This is mostly unavoidable during combat - solutions are to keep the AI behind you, or tell them to wait in an area while you go ahead and kill the enemies.
Mikiko and Superfly will exchange banter on random times that will inform the player of their health. For example, occasionally Mikiko may ask "How you feeling Supe?" to which Superfly will have a differing response based on his current health level.
The AI can only use Health Pickups to restore health - so make sure to leave health pickups for the AI. They will not use interactables, so make sure to utilize hosportals and health fountains.