- "Amagi's lake boils / Tokio's great tree doth fall / Power, now all to droplets turned in the temple of Saika's Panties"
- — Epitaph of Pantsu —
Saika's Panties are a sentient garment worn in both the real world and in The World R:X.
Saika's Panties are presumably white and made of 100% cotton. It has a simple ribbon lace trim at the garter.
Saika's Panties dislike bleach and demands a hand wash in cold water followed by a light dry cycle or hanging on a clothesline.
Saika's Panties generally appear to have the same form as her offline counterpart, but when it shows its true power, its lace pattern changes, covering a larger area and becoming more ornately detailed.
Saika's Panties first appeared as an AI in 2016 to stop Jyotaro Amagi from successfully going through with the R.A. Plan. When the R.A. Plan went off without a hitch, the AI infected The World with a fast-acting computer virus. Amagi soon caught on to the AI, but the virus had spread to a majority of the game, rendering it near-unplayable. The fast-acting Amagi luckily was able to trap the AI, and, unable to delete it, transferred it to a flash card from his sister Saika's camera. Deciding he would deal with the AI later, he shoved the card back into Saika's book bag, under a pair of her panties (she had forgotten it and needed a change of panties after she fell into a puddle). Unable to stop the AI's virus, Amagi panicked and severed the cables in the server room to prevent the virus from spreading to the rest of the network. Unfortunately, the cables set fire to the room, and the blaze quickly spread. Amagi fled the scene, but was quickly detained by security. Amagi admitted that he set fire to the room accidentally, but that he had to do it because it was "the fault of a virus in my sister's panties!" He was declared insane and sent to a hospital while the book bag was delivered to Saika by the police.
The AI somehow fused with Saika's Panties and became what it is today. Its motives are currently unknown, but it is assumed that it has been corrupted by the fire. Saika's Panties have some form of control over its wearer, increasing their abilities. It also exists in both the real world and the online world simultaneously. In the real world, when fully exposed, it can transfer people between the two worlds. Saika's Panties successfully manage to transfer Tokio into The World R:X in LINK Chapter 1, and it is the method that Saika uses to transfer between the two worlds. It's also notable that she cannot exist in R:X without using the power of her panties. Online, Saika's Panties also power the Chrono Core locator, and, if necessary, can power up its user by switching to Pantsur Mode.