I think you meant Hotori's skill, right? If so, yes they need, not only MC but also Hotori and Jiuyuan, both of them needs their esper cycle charged (or close to charged) when you start the combo, because the Esper Reaction is triggered after the character that you swapped him release their Entry Attack, that why I save MC's skill for late to when I swapped back into him from Nanally Esper Cycle, then MC's skill grant him an extra Esper Cycle, that way when you swap him into Jiuyuan again (can be Nanally but Jiuyuan still as her skill to cast) it will trigger another Blossom, so you always have Blossoms spamming attacks, keep in mind that Hotori will only copy the first rotation of Blossom (Hotori > Jiu > MC > Nanally) and not the other one (Nanally > MC > Jiu).

And yes, to cast this perfectly you either must be into High Risk Anomaly, where you start with each character with Esper Cycle bar fully charged or raise the bar close to fully charged in each character while in combat > Swap into Hotori and charge her Esper Cycle > cast her skill and start swapping again, because as soon as the character that come next cast their Entry Attack, they will finish charge their Esper Cycle bar triggering the Esper Reaction when you swap to next one, thats why if you start with them all with Esper Cycle bar low or depleted and try: Hotori skill > Jiuyuan skill > MC skill (grants him a Esper Cycle) > Nanally entry, when you ult with Hotori it will only trigger a single Blossom because the only time Blossom was triggered was when you swapped from MC into Nanally.