While this is tropey, it could match Code Lyoko (2003). It's a French cartoon though, not an anime.
Jeremy Belpois, a 12-year-old prodigy attending boarding school at Kadic Academy, discovers a quantum supercomputer in an abandoned factory near his school. Upon activating it, he discovers a virtual world called Lyoko with an artificially intelligent girl named Aelita trapped inside it. Jeremy learns of X.A.N.A., a fully autonomous, malevolent, and highly intelligent multi-agent system, that also dwells within the Supercomputer. Using Lyoko's powers, X.A.N.A can possess electronics and objects in the real world like a virus to wreak havoc. X.A.N.A.'s primary objective is to eliminate anyone aware of the Supercomputer's existence so that it will be free to conquer the real world and destroy all humanity.
Jeremy works tirelessly to materialize Aelita into the real world and stop attacks caused by X.A.N.A. Jeremy is aided by his three friends Odd Della Robbia, Ulrich Stern, and Yumi Ishiyama, who are virtualized into Lyoko to save both worlds from the sinister virtual entity.
Pink-themed Aelita can be seen at 0'35 in the opening
The monster could be any one in these... Krabs and tarantulas both have long legs, and all have X.A.N.A.'s target symbol as their "eye":