From what I can gather, his stats are:
- Active: Change board to wood, dark and hearts. Two-turn haste. 13-turn cooldown.
- Leader: 1.5x HP for Attackers. 4x ATK for Attackers after using a skill.
He looks like a solid leader alternative to Zuoh for the Meimei System. When paired with another Ishida, this two-turn haste still enables a full-board change every turn even though the cooldown is 13 turns. The biggest downside is his inferior 16x ATK bonus. However, his HP bonus does enable the full System team to enter dungeons where prohibitive preemptives — read: Divine Queen Hera — that would otherwise require swapping out a Meimei for a damage shield.
It’s also possible to use him as an alternative sub to Meimei since his board also creates hearts. This gives the team a chance to heal in dungeons with multiple preemptives without otherwise missing a step. He does break the system, though, but the team can still get a board change for 10+ turns which should be good enough in most situations.
In short, it looks like this guy can be a nice complement to existing Meimei Systems, but he isn’t essential. I think his 16x ATK bonus in particular will prevent him from from replacing Zuoh. Ishida may be on-color, but he doesn’t bring any TPAs to help bridge the damage gap further.