Golden Symbol 1 card combo (DEF Increase, guarantees blocks for 3 turns)
Unholy Symbol 4 card combo Physical 118, Light 50 (causes Paralysis, can double-turn before attack or Life Drain) Life Drain 5 card combo Physical 154, Light 65, Chrono 28 (heals self: Final Damage, double-turns after Unholy Symbol)
Physical 10, Light 8, Chrono 2 (0-4 time(s) per max combo)
Stock up on dark and wind magnus for this battle, Xelha, Kalas, and Gibari are a good team for this battle. Lyude works as well, so it's really up to you. Additionally you will be fine if you're around level 21. Sikri uses a combo ending with Unholy Symbol, which not only deals a large amount of damage, but can also paralyze, counter with anti paralysis magnus ASAP. Kalas should be able to tear this monster apart with all of his Wind Magnus. Xelha should be packed with Dark and Wind Magnus, and Gibari can fare for himself with his Wind Magnus. Near the end of the battle, Sikri will begin to use Life Drain. He will drain around 250 HP from a party member and add it to its own health. But that’s nothing you cant deal with in a single turn so that isn't a big threat to you now.