Uchuu no Stellvia, Vandread Recommendations
Both are space related with a few romances here and there. Mechs are another similarity and there is a vast exploration of planets and locations out there. Difference is one is a series and the other is a H-series, 'Vandread' actually focus on romantic scenes more often than you think and battles second. 'Uchuu no Stellvia' is a hardcore action H-series that has a bit of everything from tentacles to animals. Fighting is not the main focal point here so anyone who wants to dream of hot ladies will not be disappointed in these two series.
Both series contain sci fi themes and involves the characters protecting what they believe is dearest to them.
Both series has a lot of emphasis on the characters and how the mature over the episodes through battles, life, and experiences. Both series also contain similar art style with drama, comedy, action, and later romance.