When you rank up in a clan you get a reward depending on what you ranked up to, here's a list of the rewards from the main site. The ranks in bold give you lucky cubes.
Clan Member Rank Up Rewards:
Ore Hero (0) >> New Hero (1) - Zero Saber, Custom Mag (3 slots)
New Hero (1) >> New Hero (2) - 3DAYS Respawn Pass, Repair Kit 50% x5, Shell Supply 50% x5
New Hero (2) >> New Hero (3) - Repair Bit x30, Burst Fire Bit x30, Range Unit x30
New Hero (3) >> New Hero (4) - 5,000 UC,
[Wp] Lucky Cube ALPHANew Hero (4) >> New Hero (5) - Tengu (3 slots), Wide Beam Gun (3 slots)
New Hero (5) >> New Hero (6) - Calico Cat Ears
New Hero (6) >> New Hero (7) - Wing Plus AMJ (3 slots), EXP+30% Ticket x2
New Hero (7) >> Iron Hero (
- 5,000 UC, Cosmo Harmonics ALPHA x3
Iron Hero (
>> Iron Hero (9) - Destructor (3 slots), Bazooka (3 slots)
Iron Hero (9) >> Iron Hero (10) - Missile Barrel LGJ, UC+30% Ticket x2
Iron Hero (10) >> Iron Hero (11) - Commander Edge
Iron Hero (11) >> Steel Hero (12) - 5,000 UC,
[Ro] Lucky Cube ALPHASteel Hero (12) >> Steel Hero (13) - Cyberoid (3 slots), Drum Machinegun (3 slots)
Steel Hero (13) >> Steel Hero (14) - Prop BSJ, DROP+30% Ticket x2
Steel Hero (14) >> Steel Hero (15) - Black Rabbit Band (1 slot)
Steel Hero (15) >> Chrome Hero (16) - 5,000 UC, Plasma Gun (3 slots),
[All] Lucky Cube ALPHASource http://www.cosmicbreak.com/info/topic/news/2369